Method and system for luminescence characterisation of a semiconductor device

Abstract

Methods and systems for luminescence characterisation of semiconductor devices are provided herein In an embodiment, the method 300 for luminescence characterisation of a perovskite material 224 comprises a step 302 of exciting at least part of the perovskite material 224 with a modulated optical beam 210 to emit a modulated photoluminescence signal 226, the modulated optical beam 210 having a modulation frequency that is selected based on an estimated lifetime of the perovskite material 224 to be characterised; a step 304 of capturing the emitted modulated photoluminescence signal 226; and a step 306 of analysing a phase and / or modulation change between the modulated optical beam 210 and the modulated photoluminescence signal 226 for characterising the perovskite material 224.

Description

[0001] METHOD AND SYSTEM FOR LUMINESCENCE CHARACTERISATION OF A SEMICONDUCTOR DEVICE

[0002] TECHNICAL FIELD

[0003] This invention generally relates to a method and system for luminescence characterisation of a semiconductor device, in particular, but not exclusively, for characterising a perovskite material or a semiconductor device with at least two different materials.

[0004] BACKGROUND

[0005] Renewable energy has become more and more widely used with an aim of reducing dependency on fossil fuels, and this in turn has led to increasing demand in semiconductor devices that are used in renewal energy applications. In particular, there has been increased adoption of solar power and this has led to more efficient solar cells / photovoltaic devices. However, more suitable metrology and characterization techniques for process monitoring and optimization in semiconductor device manufacturing and failure analysis of semiconductor devices is needed.

[0006] Some technologies for probing semiconductor devices are constrained to semiconductor devices that are not metallized, while some other technologies for probing semiconductor devices may be limited to specific material, in particular silicon- based semiconductor devices. Thus, existing technologies have limited applications.

[0007] It is an object of the present invention to address problems of the prior art and / or to provide the public with a useful choice.

[0008] SUMMARY

[0009] According to a first aspect of the present invention, a method for luminescence characterisation of a perovskite material is provided. The method comprises: exciting at least part of the perovskite material with a modulated optical beam to emit a modulated photoluminescence signal, the modulated optical beam having a modulation frequency that is selected based on an estimated lifetime of the perovskite material to be characterised; capturing the emitted modulated photoluminescence signal; analysing a phase and / or modulation change between the modulated optical beam and the modulated photoluminescence signal for characterising the perovskite material.

[0010] As described in the preferred embodiment, the method allows the determination of optoelectronic properties (such as charge carrier lifetime) of perovskite materials (such as perovskite-based photovoltaic devices). By modulating the optical beam and measuring the phase change and / or modulation change of the emitted luminescence, the method is capable of retrieving systematic quantitative optoelectronic properties independent of measurement conditions, which makes it easy for benchmarking and making direct comparison across different semiconductor devices. Also, with the phase / modulation change analysis, effective carrier lifetimes of the perovskite material may be measured even if the perovskite material is partially covered by opaque layer / s (such as metal layer / s) and / or is covered by optical layer / s (whether partially or wholly), which makes the present invention applicable to semiconductor devices at different manufacturing stages including metallized devices.

[0011] In an embodiment, the modulation frequency of the modulated optical beam may be between 150 kHz and 160 MHz. Using the high modulation frequency of the optical excitation, rapid sampling and short integration times may be achieved. Hence, the perovskite material may be measured at a fast speed on the order of seconds, which makes the method being applicable to both in-depth scientific analysis and production large-scale screening.

[0012] Preferably, the emitted modulated photoluminescence signal may have a wavelength of between 600 nm and 900 nm. This range should cover most types of perovskites materials, although it would be apparent that wavelengths outside of this range may be used.

[0013] Specifically, capturing the modulated photoluminescence signal may comprise capturing one or more images of the perovskite material. The spatial resolution obtained from the captured images of the perovskite material may provide more information on the heterogeneity of the perovskite material and may be used to detect non-uniform ity.

[0014] According to a second aspect of the present invention, a system for luminescence characterisation of a perovskite material. The system comprises: an illumination module operable to generate an optical beam for exciting at least part of the perovskite material to emit a modulated photoluminescence signal, the modulated optical beam having a modulation frequency that is selected based on an estimated lifetime of the perovskite material to be characterised; a signal capturing module operable to capture the modulated photoluminescence signal; and a data processing module operable to analyse a phase and / or modulation change between the modulated optical beam and the modulated photoluminescence signal for characterising the perovskite material.

[0015] The system is capable of determining optoelectronic properties (such as charge carrier lifetime) of perovskite materials (such as perovskite-based photovoltaic devices). By modulating the optical beam and measuring the phase change and / or modulation change of the emitted luminescence, the system is capable of retrieving systematic quantitative optoelectronic properties independent of measurement conditions, which makes it easy for benchmarking and making direct comparison across different semiconductor devices. Also, with the phase / modulation change analysis, effective carrier lifetimes of the perovskite material may be measured even if the perovskite material is partially covered by opaque layer / s (such as metal layer / s) and / or is covered by optical layer / s (whether partially or wholly), which makes the present invention applicable to semiconductor devices at different manufacturing stages including metallized devices.

[0016] In an embodiment, the modulation frequency of the modulated optical beam may be between 150 kHz and 160 MHz. It would be apparent that, as described in the detailed embodiment, the derived modulation frequency may thus be any value / frequency within this range. Equipped with an optical excitation at a high modulation frequency, the system is capable of rapid sampling so that short integration times may be achieved. Hence, the system may be used to measure perovskite material at a fast speed on the order of seconds, which makes the system being applicable to both in- depth scientific analysis and production large-scale screening.

[0017] In an embodiment, the emitted modulated photoluminescence signal has a wavelength of between 600 nm and 900 nm. This range should cover most types of perovskites materials, although it would be apparent that wavelengths outside of this range may be used. It would also be apparent that, as described in the detailed embodiment, the wavelength of the emitted modulated photoluminescence signal may have any value / wavelength within this range.

[0018] Preferably, the signal capturing module may comprise a frequency-domain fluorescence lifetime imaging camera. The camera provides spatial resolution of the perovskite material to the system, which empowers the system the ability to detect heterogeneity or non-uniform ity of the perovskite material.

[0019] According to a third aspect of the present invention, there is provided a method for luminescence characterisation of a semiconductor device comprising a first semiconductor material and a second semiconductor material, the method comprises: exciting at least part of the first semiconductor material with a first modulated optical beam to emit a first modulated photoluminescence signal; exciting at least part of the second semiconductor material with a second modulated optical beam to emit a second modulated photoluminescence signal; capturing the emitted first modulated photoluminescence signal and the emitted second modulated photoluminescence signal for respectively characterising the first semiconductor material based on the first modulated optical beam and the emitted first modulated photoluminescence signal and the second semiconductor material based on the second modulated optical beam and the emitted second modulated photoluminescence signal, wherein the first modulated optical beam and the second modulated optical beam are modulated at different frequencies and / or have different excitation wavelengths.

[0020] With the use of differently modulated optical beams to excite different materials of the semiconductor device, effective responses from materials of different lifetime scales and / or emission wavelengths are separated, which makes it applicable for probing materials / devices when more than two types of optoelectronic materials / devices are present (e g. probing perovskite sub-cells and Si sub-cells in a perovskite / Si tandem devices).

[0021] Specifically, capturing the emitted first modulated photoluminescence signal may be performed after exciting the at least part of the first semiconductor material with the first modulated optical beam, but before exciting the at least part of the second semiconductor material with the second modulated optical beam. This helps to better separate the first modulated photoluminescence signal and second modulated photoluminescence signal for respectively characterising the two semiconductor materials.

[0022] Preferably, an exposure time of the at least part of the first semiconductor material being illuminated by the first modulated optical beam may be in a range from 1 ms to 2 seconds. With such short exposure time, measurements are allowed to be completed within seconds which makes this method suitable for production monitoring, this also help to avoid the risk of saturating the device for capturing the photoluminescence signals.

[0023] In a specific application, the first semiconductor material and the second semiconductor material may be in a tandem configuration and characterising the first semiconductor material and the second semiconductor material may comprise determining a distribution of the first semiconductor material over the second semiconductor material. For a semiconductor device in a tandem configuration, different materials may affect the detecting results of each other. This method may be useful to detect different semiconductor materials and characterise them respectively, such as determining a distribution of the first semiconductor material over the second semiconductor material, which is helpful at occasions such as during producing the tandem device and monitoring the quality of the products.

[0024] In an embodiment, the method may further comprise exciting at least part of the second semiconductor material to emit a third bias photoluminescence signal; capturing the third bias photoluminescence signal for characterising the second semiconductor material based on the third bias optical beam and the third bias photoluminescence signal. The third excitation may set a condition for characterising the second semiconductor material using the second modulated optical beam and the emitted second modulated photoluminescence signal.

[0025] Advantageously, capturing the first modulated photoluminescence signal may comprise capturing one or more images of the first semiconductor material, and / or capturing the second modulated photoluminescence signal may comprise capturing one or more images of the second semiconductor material. The spatial resolution obtained from the captured images may provide more information on the heterogeneity of the semiconductor materials and may be used to detect non-uniform ity.

[0026] Preferably, the first modulated optical beam may have a modulation frequency of between 150 kHz and 160 MHz. With the high modulation frequency, the method is capable of rapid sampling so that short integration times may be achieved. This allows the method to measure the first semiconductor material at a fast speed on the order of seconds, which makes the method being applicable to both in-depth scientific analysis and production large-scale screening. Such frequency also enables the method to cover materials like perovskites.

[0027] In an embodiment, the first modulated photoluminescence signal may be captured at a wavelength of between 600 nm and 900 nm, which covers most types of perovskite materials.

[0028] Preferably, the method may further comprise analysing a phase and / or modulation change between the first modulated photoluminescence signal and the first optical beam for characterising the first semiconductor material. The method may further comprise analysing a phase and / or modulation change between the second modulated photoluminescence signal and the second modulated optical beam for characterising the second semiconductor material. By modulating the optical beam and measuring the phase change and / or modulation change of the emitted luminescence, the method is capable of retrieving systematic quantitative optoelectronic properties independent of measurement conditions, which makes it easy for benchmarking and making direct comparison across different semiconductor devices. Also, with the phase / modulation change analysis, effective carrier lifetimes of the both semiconductor materials may be measured even if there are metal and / or additional optical layers partially cover the perovskite material, which makes the present method applicable to semiconductor devices at different manufacturing stages including metallized devices. The proposed solution is applicable to both nonmetallized and metallized tandem samples at different stages, which makes the solution applicable to all manufacturing stages of the semiconductor devices.

[0029] According to a fourth aspect of the present invention, there is provided a system for luminescence characterisation of a semiconductor device comprising a first semiconductor material and a second semiconductor material. The system comprises: a first illumination module operable to generate a first modulated optical beam for exciting at least part of the first semiconductor material to emit a first modulated photoluminescence signal; a second illumination module operable to generate a second modulated optical beam for exciting at least part of the second semiconductor material to emit a second modulated photoluminescence signal; a first signal capturing module operable to capture the first modulated photoluminescence signal; a second signal capturing module operable to capture the second modulated photoluminescence signal; and a data processing module operable to analyse the first modulated optical beam and the first modulated photoluminescence signal for characterising the first semiconductor material, and to analyse the second modulated optical beam and the second modulated photoluminescence signal for characterising the second semiconductor material, wherein the first modulated optical beam and the second modulated optical beam are modulated at different frequencies and / or have different excitation wavelengths. As described in the preferred embodiment, the system may be useful to separate effective responses from materials of different lifetime scales and emission wavelengths by modulating optical beams differently to excite different materials of the semiconductor device. Further, the system may be useful to probe materials / devices having two or more types of optoelectronic materials / devices (e.g. probing perovskite sub-cells and Si sub-cells in a perovskite / Si tandem devices). Advantageously, the first semiconductor material and the second semiconductor material may be in a tandem configuration and the data processing module may be operable to characterise the first semiconductor material and the second semiconductor material to determine a distribution of the first semiconductor material over the second semiconductor material. For a semiconductor device in a tandem configuration, different materials may affect the detecting results of each other. This system helps to detect different semiconductor materials and characterise them respectively, such as determining a distribution of the first semiconductor material over the second semiconductor material, which is helpful at occasions such as during producing the tandem device and monitoring the quality of the products.

[0030] Preferably, the system may further comprise a third illumination module operable to be biased to generate a third bias optical beam for exciting the at least part of the second semiconductor material to emit a third bias photoluminescence signal, wherein the second signal capturing module may be operable to capture the third bias photoluminescence signal, wherein the data processing module is operable to analyse the second modulated optical beam, the second modulated photoluminescence signal, the third bias optical beam and the third bias photoluminescence signal to characterise the second semiconductor material. The third illumination module may set a condition for characterising the second semiconductor material using the second modulated optical beam and the emitted second modulated photo luminescence signal.

[0031] Specifically, the first modulated optical beam may have a modulation frequency of between 150 kHz and 160 MHz. With such high modulation frequencies, the system is capable of rapid sampling so that short integration times may be achieved. This allows the system to measure the first semiconductor material at a fast speed on the order of seconds, which makes the system being applicable to both in-depth scientific analysis and production large-scale screening. Such frequencies also enable the system to cover materials like perovskites.

[0032] Preferably, the first signal capturing module may be sensitive in a wavelength range from 600nm to 900nm. Such first signal capturing module empowers the system the ability to characterise most types of perovskite materials. In an embodiment, the second modulated optical beam may have a modulation frequency of 100Hz to 100kHz. Such frequency enables the system to cover materials like silicon.

[0033] Preferably, the first signal capturing module may comprise a frequency-domain fluorescence lifetime imaging camera. In an embodiment, the second signal capturing module may comprise a frequency-domain fluorescence lifetime imaging camera or a short-wave infrared InGaAs camera. The camera may provide spatial resolution of the perovskite material to the system, which empowers the system with the ability to detect heterogeneity or non-uniform ity of the perovskite material.

[0034] It would be apparent that features relating to one aspect / embodiment may be applicable and used interchangeably with features relating to the other aspects / embodiments.

[0035] BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Fig. 1 depicts a general block diagram of a system for luminescence characterisation of a semiconductor device;

[0037] Fig. 2 depicts schematics of a first embodiment for realizing the system of Fig. 1 for luminescence characterisation of a semiconductor device comprising a perovskite cell;

[0038] Fig. 3 depicts a diagram a method for charactering a semiconductor device comprising a perovskite cell using the first embodiment of Fig. 2;

[0039] Fig. 4 depicts schematics of a second embodiment for realizing the system of Fig. 1 for luminescence characterisation of a semiconductor device comprising a perovskite cell;

[0040] Figs. 5(a)-(b) depict two statues of some parts of schematics of a third embodiment for realizing the system of Fig. 1 . Figs. 6(a)-(b) depict two statuses of some parts of schematics of a fourth embodiment for realizing the system of Fig. 1 ;

[0041] Fig. 7 depicts a diagram illustrating main functional steps of a method for charactering a semiconductor device comprising a perovskite cell and a silicon cell using the fourth embodiment of Figs. 6(a) and 6(b);

[0042] Figs. 8(a)-8(f) depict images of a perovskite sample generated using the method of Fig. 3 with a modulation frequency of 400 kHz and an exposure time of 2ms;

[0043] Figs. 9(a)-9(f) depict images of a perovskite cell in a perovskite / silicon tandem device sample generated using the method of Fig. 7 with a modulation frequency of 400 kHz and an exposure time of 50ms;

[0044] Figs. 10(a)-10(e) depicts images of a perovskite cell in another perovskite / silicon tandem device sample generated using the method of Fig. 7, with a modulation frequency of 400 kHz and an exposure time of 600ms;

[0045] Fig. 11 is a table illustrating some examples of semiconductor devices with multijunction solar cells that the method of Fig. 7 may be used to characterise.

[0046] DETAILED DESCRIPTION

[0047] This disclosure provides systems and methods for luminescence characterisation of a semiconductor device. The semiconductor device comprises one or more materials selected from a group of materials comprising perovskite, silicon, Cadmium Telluride (CdTe), germanium (Ge), Copper Indium Gallium Selenide (CIGS), Copper Zinc Tin Sulfide (CZTS), indium phosphide (InP), gallium arsenide (GaAs), gallium indium phosphide (GalnP) and other lll-V semiconductor materials etc. Fig. 1 depicts a general block diagram of a system 100 for luminescence characterisation of a semiconductor device. The system 100 comprises a controlling module 102, a modulation module 104, an illumination module 106, a data processing module 108 and a signal capturing module 110. The modulation module 104 is operable to modulate optical beams generated by the illumination module 106 at desired frequency and / or intensity. The signal capturing module 110 is operable to capture optical signals, such as photoluminescence signals emitted from the semiconductor device. The data processing module 108 processes the data captured by the signal capturing module 110 and yield the characterisation results. The controlling module 102 is operable to control operation of the other modules, such as controlling the modulation module 104 to modulate optical beams generated by the illumination module 106 to generate desired optical beams, controlling the data processing module 108 to process signal captured by the signal capturing module 110.

[0048] Fig. 2 depicts schematics of a first embodiment 200 for realizing the system 100 for photoluminescence and lifetime imaging a semiconductor device 222 comprising a perovskite cell 224. In this embodiment, the controlling module 102 comprises a desktop computer 202, the modulation module 104 comprises a fast modulator 204, the illumination module 106 comprises an optical module 206 and an excitation filter 208, the data processing module 108 comprises a data acquisition card (DAQ Card) 212, a lock-in amplifier 214 and a preliminary amplifier 216, and the signal capturing module 110 comprises a camera 218 and a luminescence filter 220. The fast modulator 204 is operable to modulate the optical module 206. The optical module 206 is modulated to generate a modulated optical beam 210 with a sinusoidally modulated illumination intensity. The excitation filter 208 filters the sinusoidally modulated optical beam 210 emitted from the optical module 206 for illuminating at least part of the perovskite cell 224 of the semiconductor device 222. Specifically, a photosensitive region of the perovskite cell 224 is excited to generate charge carriers, which then recombine to emit a modulated photoluminescence signal 226. The sinusoidally modulated optical beam 210 has a modulation frequency in a range from 150 kHz to 160 MHz, preferably 160kHz to 160MHz, more preferably 200kHz to 100MHz, more preferably 200kHz to 40MHz, more preferably 500kHz to 70MHz, more preferably 1MHz to 60MHz, more preferably 10MHz to 50MHz, even more preferably 20MHz to 40MHz, or particular frequency within any of these frequency ranges. A preferred modulation frequency may be determined using equation (1 ) where T is an estimated carrier lifetime. Different types of perovskite material may have different estimated carrier lifetimes. Thus, different types of perovskite materials with different estimated carrier lifetime would require respective modulation frequency based on the estimated lifetime of that type of the perovskite materials. The carrier lifetime of perovskites is influenced by factors such as composition, material quality, and environmental conditions. For example, a freshly prepared sample may have a lifetime of a few hundred nanoseconds. However, if left in ambient conditions without proper encapsulation, the sample can degrade, and its lifetime may drop to just a few tens of nanoseconds within a few days. The carrier lifetime may be estimated in various manners, for example: it may be estimated based on one’s prior experience; it may be measured using techniques like time-resolved photoluminescence (TRPL); it may be determined experimentally by varying modulation frequencies and analysing the corresponding results etc. The camera 218 is a high-speed and high-resolution camera sensitive in a wavelength range from visible to near infrared wavelength, e.g. from 600 nm to 900 nm. Specifically, in this embodiment, the camera 218 is a frequency-domain fluorescence lifetime imaging (FD-FLIM) camera operable to capture images for photoluminescence and lifetime imaging of the perovskite cell 224 at a wavelength of 600 nm to 900 nm. The camera 218 is operable to register emitted modulated photoluminescence signal up to the modulation frequency ranges discussed above.

[0049] Fig. 3 depicts a diagram illustrating main functional steps of a method 300 for luminescence characterisation of the semiconductor device 222 comprising the perovskite cell 224 using the first embodiment 200 of Fig. 2. The method 300 comprises a step 302 of exciting at least part of the perovskite cell 224 with the optical beam 210 to emit the modulated photoluminescence signal 226. Source of the optical beam 210 is modulated at a frequency that is selected based on an estimated lifetime of the perovskite cell 224, in the range from 150 kHz to 160 MHz, preferably 160kHz to 160MHz, more preferably 200kHz to 100MHz, more preferably 200kHz to 40MHz, more preferably 500kHz to 70MHz, more preferably 1 MHz to 60MHz, more preferably 10MHz to 50MHz, even more preferably 20MHz to 40MHz, or particular frequency within any of these frequency ranges. Source of the optical beam 210 is also modulated to have the sinusoidally modulated illumination intensity. Being illuminated by the sinusoidally modulated optical beam 210, the photosensitive region of the at least part of the perovskite cell 224 is excited to generate charge carriers, which then recombine to emit the modulated photoluminescence signal 226. The method 300 further comprises a step 304 of capturing the emitted modulated photoluminescence signal 226. The method 300 further comprises step 306 of analysing a phase and / or modulation change between the modulated optical beam 210 and the modulated photoluminescence signal 226 for characterising the perovskite cell 224.

[0050] The camera 218 is operable to capture the modulated photoluminescence signal 226, and generate one or more spatial images of the at least part of the perovskite cell 224. In this embodiment, the camera 218 is a FD-FLIM camera having a resolution of 1008 * 1008 pixels or above, which is high enough to makes it possible to differentiate the grains (in hundreds of nm) of perovskite materials. The camera 218 is also capable of measuring lifetime in a few ns. The preliminary amplifier 216, the lock-in amplifier 214 and the DAQ Card 212 are operable to receive and process modulated photoluminescence signal 226 captured by the camera 218. In this embodiment, the modulated photoluminescence signal 226 has a wavelength of between 600nm and 900nm. The processed signal is provided to the desktop computer 202 for further processing to evaluate the characteristics of the semiconductor device 222. By measuring a phase and / or modulation difference between the excitation and photoluminescence, the effective carrier lifetimes of the perovskite cell 224 is calculated.

[0051] The emitted luminescence signal l(t) after time t is given by equation (2). where T is carrier lifetime, t is the time passed after the excitation (whether the illumination is constant or pulse).

[0052] The relationship between the phase change cp and phase lifetime is depicted in equation (3) p — Arctan (t r) (3) where T is phase lifetime, co is an angular frequency calculated using co = 2TTf , where f is a modulation frequency. The modulation index M is defined by equation (4) where Aexcitaionis an amplitude of an optical excitation, Sexcitaionis an average signal of the optical excitation, Aemissionis an amplitude of an emission, Semissionis an average signal of the emission.

[0053] The relationship between the modulation index M and modulation lifetime is depicted in equation (5)

[0054] M2= 1 / (1 + (<DT)2) (5)

[0055] Where T is modulation lifetime, co is the angular frequency.

[0056] After the phase and modulation are detected using the signal capturing module 110, phase lifetime and modulation lifetime can be calculated according to the above equations respectively. If the perovskite materials show single-exponential decay, the phase lifetime would be equal to the modulation lifetime; if the perovskite materials show multi-exponential decay, the phase lifetime would be different from the modulation lifetime.

[0057] By using the above method 300, with a signal capturing module that can register meaningful phase / modulation change, effective carrier lifetimes of the perovskite cell 224 of the semiconductor device 222 can be measured even if the perovskite cell 224 is partially covered by opaque layer / s (such as metal layer / s) and / or is covered by optical layer / s (whether partially or wholly), which makes the present invention applicable to semiconductor devices at different manufacturing stages including metallized devices. Using the high modulation frequency (typically in kHz and MHz as discussed above) of the optical excitation, rapid sampling and short integration times can be achieved. Hence, semiconductor devices may be measured at a fast speed on the order of seconds, which makes the system 200 and method 300 being applicable to both in-depth scientific analysis and production large-scale screening. In contrast, time-domain measurements require pulsed excitation and time-gated detection, which typically takes longer measurement time. By modulating illumination intensity of the optical beam sinusoidally and measuring the phase change and modulation change of the emitted luminescence, the system and method are capable of retrieving systematic quantitative optoelectronic properties independent of measurement conditions, which makes it easy for benchmarking and making direct comparison across different semiconductor devices. The imaging capability provides a means to evaluate and quantify the relevant characteristics over the perovskite-based semiconductor device, which offers valuable insights to the uniformity of perovskite materials and devices. By capturing a plurality of images of the semiconductor device, the present invention can obtain both time-resolved and spatially resolved information for evaluating and quantifying the characteristics of the semiconductor device both over device area and over time, allowing both stability and uniformity analysis. With determination of spatially resolved optoelectronic properties (such as charge carrier lifetime), the method provides information on the heterogeneity of the material to be measured, which is particularly advantageous when measuring perovskites materials that are typically non-uniform. Further, as the system allows the registration of the modulated luminescence signal at each pixel of the camera concurrently, the present invention allows an integration with an imaging system in both microscopic and wide field configuration, the present invention has the flexibility to integrate in a microscopic configuration so as to investigate micro-structural characteristics or in a wide-field configuration so as to investigate large area device , which is particularly useful for industrial application. Overall speaking, the proposed approach is fast, versatile, and suitable for in-depth characterization, material inspection as well as process monitoring, especially for perovskite and related optoelectronic devices regardless of whether metalized or not.

[0058] Using the high modulation frequency of the optical excitation, rapid sampling and short integration times may be achieved, the method 300 is faster in evaluating and quantifying the relevant characteristics of semiconductor devices, compared to conventional methods like measuring the transient photoluminescence decay using streak cameras or time-correlated single photon counting. The method 300 may allow measurements to be done in a few seconds. In addition, the method 300 is less affected by various measurement conditions and material attributes, compared to methods like measuring steady-state photoluminescence (PL) which can also be used to infer carrier lifetime.

[0059] Fig. 4 depicts schematics of a second embodiment 400 for realizing the system 100 for photoluminescence and lifetime measurement of a semiconductor device 422 comprising a perovskite cell 424. In this embodiment, the controlling module 102 comprises a desktop computer 402, the modulation module 104 comprises a fast modulator 404, the illumination module 106 comprises a optical module 406 and an excitation filter 408, the data processing module 108 comprises a DAQ Card 412, a lock-in amplifier 414 and a preliminary amplifier 416, and the signal capturing module 110 comprises a detector 418 and a luminescence filter 420. The fast modulator 404 is operable to modulate the optical module 406. The optical module 406 is modulated to generate sinusoidally modulated optical beam 410 with a sinusoidally modulated illumination intensity. The excitation filter 408 filters the sinusoidally modulated optical beam 410 emitted from the optical module 406 for illuminating at least part of the perovskite cell 424. Specifically, a photosensitive region of the at least part of the perovskite cell 424 is excited to generate charge carriers, which then recombine to emit a modulated luminescence signal 426. The sinusoidally modulated optical beam 410 has a frequency in the range from 150 kHz to 160 MHz, preferably 160kHz to 160MHz, more preferably 200kHz to 100MHz, more preferably 200kHz to 40MHz, more preferably 500kHz to 70MHz, more preferably 1 MHz to 60MHz, more preferably 10MHz to 50MHz, even more preferably 20MHz to 40MHz, or particular frequency within any of these frequency ranges. The detector 418 comprises a photo diode, which is sensitive in a wavelength range from visible to near infrared wavelength, e.g. a wavelength range from 600 nm to 900 nm. The detector 418 is operable to capture the modulated luminescence signal 426. The optical preliminary amplifier 416, the lock-in amplifier 414 and the DAQ Card 412 receive and process the modulated luminescence signal 426 captured by the detector 418. The processed signal is provided to the desktop computer 402 for further processing to evaluate the characteristics of the se iconductor device 422.

[0060] It is appreciated from the above that, comparing to the first embodiment 200, the second embodiment 400 replaces the camera 218 of the first embodiment 200 with a detector, so that the method 300 described above and depicted in Fig. 3 for charactering the semiconductor device 222 can be adaptively adjusted for charactering the semiconductor device 422 using the second embodiment 400. After the at least part of the perovskite cell 424 is illuminated to excite the modulated photoluminescence signal 426. The method comprises a step of capturing the modulated photoluminescence signal 426 emitted from the at least part of the perovskite cell 424 using the detector 418. By capturing the modulate photoluminescence signal 426, the detector 418 generates luminescence data of the at least part of the perovskite cell 424. Equations (1)-(5) may be used to process the luminescence data to characterise the semiconductor device 422.

[0061] Figs. 5(a) and 5(b) depict some parts of schematics of a third embodiment 500 for realizing the system 100 for luminescence characterisation of a semiconductor device 502 comprising a first semiconductor material 504 and a second semiconductor material 506 in two working statuses respectively. As shown in Figs. 5(a) and 5(b), the two semiconductor materials are arranged in a tandem configuration, with the first semiconductor material 504 being configured to be a top layer of the semiconductor device 502, and the second semiconductor material 506 being configured to be a bottom layer beneath the first semiconductor material 504. In this embodiment, the illumination module 106 comprises a first optical module 508, a second optical module 510, a first excitation filter 512, a second excitation filter 514, and the signal capturing module 110 comprises a first camera 516, a second camera 518, a first luminescence filter 520 and a second luminescence filter 522. The first excitation filter 512 and the second excitation filter 514 are operable to filter light generated by the first optical module 508 and the second optical module 510 respectively. The first luminescence filter 520 and the second luminescence filter 522 are operable to filter luminescence signals to be captured by the first camera 516 and the second camera 518 respectively. Figs. 5(a) and 5(b) merely illustrate the main optical excitation sources and cameras required for performing luminescence and lifetime imaging, other parts and components of the system 100 may be required and realised in the same way as any of the above embodiments or other appropriate manners known in the art. Fig. 5(a) depicts the third embodiment 500 when the first optical module 508 and the first camera 516 are activated for probing the first semiconductor material 504. The first optical module 508 is modulated to generate a first modulated optical beam 524 for illuminating at least part of the first semiconductor material 504. The first modulated optical beam 524 is modulated to have a sinusoidally modulated illumination intensity with a frequency in a range from 10 Hz to 160 MHz, preferably 100Hz to 160MHz, more preferably 1 kHz to 160MHz, more preferably 100kHz to 160MHz, more preferably 150kHz to 160MHz, more preferably 160kHz to 160MHz, more preferably 200kHz to 100MHz, more preferably 500kHz to 70MHz, more preferably 1MHz to 60MHz, more preferably 10MHz to 50MHz, more preferably 20MHz to 40MHz, more preferably 100Hz to 100kHz, more preferably 100Hz to 50kHz, more preferably 1 kHz to 50kHz, more preferably 10kHz to 40kHz, more preferably 1MHz to 160Mhz, more preferably 150kHz to 2MHz, more preferably 1 MHz to 16MHz, more preferably 150kHz to 1 MHz, more preferably 1 MHz to 16MHz, more preferably 10Hz to 10kHz or particular frequency within any of these frequency ranges. The first modulated optical beam 524 has an excitation wavelength in a range from 300 nm to 1700 nm, preferably 300 nm to 1200 nm, more preferably 300 nm to 1000 nm, more preferably 300 nm to 800 nm, more preferably 300 nm to 600 nm, even more preferably 700 nm to 800 nm, or particular wavelength within any of these wavelength ranges. The first camera 516 is a high-speed and high-resolution camera. Being illuminated by the first modulated optical beam 524, a photosensitive region of at least part of the first semiconductor material 504 is excited to generate charge carriers, which then recombine to emit corresponding a first modulated photoluminescence signal 526. The first camera 516 is operable to capture the first modulated photoluminescence signal 526 and generate one or more images of the first semiconductor material 504. The one or more images generated by the first camera 516 may be processed to characterise the first semiconductor material 504, such as comparing a phase and / or modulation difference between the first modulated optical beam 524 and the first modulated photoluminescence signal 526. The above mentioned method of analysing the phase and / or modulation change using equations (1 )-(5) may be used here for the analysis and characterising the first semiconductor material 504. The first modulated photoluminescence signal 526 has an emission / detection wavelength in a range of 600 nm to 2000 nm, preferably 600 nm to 1300 nm, more preferably 600 nm to 1200 nm, more preferably 600 nm to 1000 nm, more preferably 600 nm to 900 nm, more preferably 600 nm to 800 nm, more preferably 800 nm to 1000 nm, more preferably 800 nm to 900 nm, more preferably 1000 nm to 1200 nm, more preferably 1700 nm to 2000 nm, or particular wavelength within any of these wavelength ranges.

[0062] Fig. 5(b) depicts the third embodiment 500 when the second optical module 510 and the second camera 518 are activated for probing the second semiconductor material 506. The second optical module 510 is modulated to generate a second modulated optical beam 528 for illuminating at least part of the second semiconductor material 506. The second modulated optical beam 528 has a sinusoidally modulated illumination intensity, with a frequency in a range from 10 Hz to 160 MHz, preferably 100Hz to 160MHz, more preferably 1 kHz to 160MHz, more preferably 100kHz to 160MHz, more preferably 150kHz to 160MHz, more preferably 160kHz to 160MHz, more preferably 200kHz to 100MHz, more preferably 500kHz to 70MHz, more preferably 1 MHz to 60MHz, more preferably 10MHz to 50MHz, more preferably 20MHz to 40MHz, more preferably 100Hz to 100kHz, more preferably 100Hz to 50kHz, more preferably 1 kHz to 50kHz, more preferably 10kHz to 40kHz, more preferably 1 MHz to 160Mhz, more preferably 150kHz to 2MHz, more preferably 1 MHz to 16MHz, more preferably 150kHz to 1MHz, more preferably 1 MHz to 16MHz, more preferably 10Hz to 10kHz or particular frequency within any of these frequency ranges. The second modulated optical beam 528 has an excitation wavelength in a range from 300 nm to 1700 nm, preferably 300 nm to 1200 nm, more preferably 300 nm to 1000 nm, more preferably 300 nm to 800 nm, more preferably 300 nm to 600 nm, even more preferably 700 nm to 800 nm, or particular wavelength within any of these wavelength ranges. Modulation of the first modulated optical beam 524 and the second modulated optical beam 528 are different in at least one of modulation frequency and excitation wavelength. Being illuminated by the second modulated optical beam 528, a photosensitive region of the at least part of the second semiconductor material 506 is excited to generate charge carriers, which then recombine to emit photoluminescence signals. When the second semiconductor material 506 is excited by the second modulated optical beam 528, the second semiconductor material 506 emits a second photoluminescence signal 530. The second camera 518 is operable to capture the second photoluminescence signal 530 and generate one or more images of the second semiconductor material 506. The one or more images generated by the second camera 518 may be processed to characterise the second semiconductor material 506, such as comparing a phase and / or modulation difference between the second modulated optical beam 528 and the second modulated photoluminescence signal 530, according to equations (1 )-(5). The second modulated photoluminescence signal 530 has an emission / detection wavelength in a range of 600 nm to 2000 nm, preferably 600 nm to 1300 nm, more preferably 600 nm to 1200 nm, more preferably 600 nm to 1000 nm, more preferably 600 nm to 900 nm, more preferably 600 nm to 800 nm, more preferably 800 nm to 1000 nm, more preferably 800 nm to 900 nm, more preferably 1000 nm to 1200 nm, more preferably 1700 nm to 2000 nm, or particular wavelength within any of these wavelength ranges.

[0063] The first semiconductor material 504 and the second semiconductor material 506 are different materials, and at least one of the parameters (e.g. modulation frequency, excitation wavelength, detection wavelength etc.) are set differently.

[0064] Figs. 6(a) and 6(b) depict some parts of schematics of a fourth embodiment 600 for realizing the system 100 for luminescence characterisation of a semiconductor device 602 comprising a silicon cell 604 and a perovskite cell 606 in two working statuses. As shown in Figs. 6(a) and 6(b), the silicon cell 604 and the perovskite cell 606 are in a tandem configuration, with the perovskite cell 606 being configured to be a top layer of the semiconductor device 602, and the silicon cell 604 being configured to be a bottom layer beneath the perovskite cell 606. In this embodiment, the illumination module 106 comprises a first optical module 608, a second optical module 610, a third optical module 612, a first excitation filter 614 and a second excitation filter 616, and the signal capturing module 110 comprises a first camera 618, a second camera 620, a first luminescence filter 622 and a second luminescence filter 624. The first excitation filter 614 and the second excitation filter 616 are operable to filter light generated by the first optical module 608 and the second optical module 610 respectively. The first luminescence filter 622 and the second luminescence filter 624 are operable to filter luminescence signals to be captured by the first camera 618 and the second camera 620 respectively. Figs. 6(a) and 6(b) merely illustrate the main optical excitation sources and cameras required for performing luminescence and lifetime imaging, other parts and components of the system 100 may be required and realised in the same way as any of the above embodiments or other appropriate manners known in the art.

[0065] Fig. 6(a) depicts the fourth embodiment 600 when the first optical module 608 and the first camera 618 are activated for probing the perovskite cell 606. The first optical module 608 is modulated to generate a first modulated optical beam 626 for illuminating at least part of the perovskite cell 606. The first modulated optical beam 626 is modulated to have a sinusoidally modulated illumination intensity with a frequency in a range from 150 kHz to 160 MHz. preferably 160kHz to 160MHz, more preferably 200kHz to 100MHz, more preferably 200kHz to 40MHz, more preferably 500kHz to 70MHz, more preferably 1 MHz to 60MHz, more preferably 10MHz to 50MHz, even more preferably 20MHz to 40MHz, or particular frequency within any of these frequency ranges. The first camera 618 is a high-speed and high-resolution camera sensitive in a wavelength range from visible to near infrared wavelength, e.g. from 600 nm to 900 nm. Being illuminated by the first modulated optical beam 626, a photosensitive region of at least part of the perovskite cell 606 is excited to generate charge carriers, which then recombine to emit corresponding a first modulated photoluminescence signal 628. The first camera 618 is operable to capture the first modulated photoluminescence signal 628 and generate one or more images of the perovskite cell 606. The one or more images generated by the first camera 618 may be processed to characterise the perovskite cell 606, such as comparing a phase and / or modulation difference between the first modulated optical beam 626 and the first modulated photoluminescence signal 628. Equations (1 )-(5) are also applicable charactering the perovskite cell 606 based on the captured signals.

[0066] Fig. 6(b) depicts the fourth embodiment 600 when the second optical module 610, the third optical module 612 and the second camera 620 are activated for probing the silicon cell 604. The second optical module 610 is modulated to generate a second modulated optical beam 630 for illuminating at least part of the silicon cell 604. The second modulated optical beam 630 has a sinusoidally modulated illumination intensity. The frequency of the second modulated optical beam 630 is in the range of 10Hz to 100kHz, preferably 100Hz to 100kHz, more preferably 100Hz to 50kHz, more preferably 1 kHz to 50kHz, more preferably 10kHz to 40kHz, even more preferably 10Hz to 10kHz. The third optical module 612 is biased to generate a third bias optical beam 632 for illuminating the at least part of the silicon cell 604. The third bias optical beam 632 has a constant illumination intensity. The third bias optical beam 632 conditions the silicon cell 604 to a particular operation condition (e g. 1 sun, 2 suns) for measuring carrier lifetime using the second modulated optical beam 630. The sensitive wavelength range of the Silicon camera is around 1000 nm to 1200 nm. Being illuminated by the second modulated optical beam 630 and / or the third bias optical beam 632, a photosensitive region of the at least part of the silicon cell 604 is excited to generate charge carriers, which then recombine to emit photoluminescence signals. When the silicon cell 604 is excited by both the second modulated optical beam 630 and the third bias optical beam 632 at the same time, the photoluminescence signal 634 emitted from the silicon cell 604 comprise a second modulated photoluminescence signal 634a corresponding to the second modulated optical beam 630 and a bias photoluminescence signal 634b corresponding to the third bias optical beam 632. The second camera 620 is operable to capture the photoluminescence signal 634 and generate one or more images of the silicon cell 604. The one or more images generated by the second camera 620 may be processed to characterise the silicon cell 604, such as comparing a phase and / or modulation difference between the second modulated optical beam 630 and the second modulated photoluminescence signal 634a according to equations (1 )-(5).

[0067] Fig. 7 depicts a diagram illustrating main functional steps of a method 700 for characterising the semiconductor device 602 comprising the perovskite cell 606 and the silicon cell 604 using the fourth embodiment 600 of Figs. 6(a) and 6(b). The method 700 comprises a step 702 of exciting at least part of the perovskite cell 606 with the first modulated optical beam 626. The first modulated optical beam 626 is modulated so that when the at least part of the perovskite cell 606 is being illuminated by the first modulated optical beam 626, a photosensitive region of the at least part of the perovskite cell 606 is excited to generate charge carriers, which then recombine to emit the first modulated photoluminescence signal 628. The method 700 further comprises a step 704 of capturing the first modulated photoluminescence signal 628 excited by the at least one part of the perovskite cell 606 for characterising the perovskite cell 606. The method 700 further comprises a step 706 of exciting at least part of the silicon cell 604 with the second modulated optical beam 630. The second modulated optical beam 630 is modulated so that when the at least part of the silicon cell 604 is being illuminated by the second modulated optical beam 630, a photosensitive region of the at least part of the silicon cell 604 is excited to generate charge carriers, which then recombine to emit the second modulated photoluminescence signal 634a. The method 700 further comprises a step 708 of capturing the second modulated photoluminescence signal 634a for characterising the silicon cell 604. The first optical module 608 and the second optical module 610 are modulated in different manners, so that the first modulated optical beam 626 and the second modulated optical beam 630 are distinguished to each other. In this embodiment, the first modulated optical beam 626 is modulated at a frequency of 150kHz to 160MHz; the second optical modulated optical beam 630 is modulated at a frequency of 100Hz to 100KHz.

[0068] The method 700 further comprises analysing the first modulated optical beam 626 and the first modulated photoluminescence signal 628 for characterising the perovskite cell 606. The method 700 further comprises analysing the second modulated optical beam 630 and the second modulated photoluminescence signal 634a for characterising the silicon cell 604. The first modulated optical beam 626 and the second modulated optical beam 630 are modulated with different frequencies. By comparing a phase and / or modulation difference between the first modulated optical beam 626 and the first modulated photoluminescence signal 628, effective charge carrier lifetime of the perovskite cell 606 may be evaluated. Similarly, by comparing a phase and / or modulation difference between the second modulated optical beam 630 and the second modulated photoluminescence signal 634a, effective charge carrier lifetime of the silicon cell 604 may be evaluated, according to equations (1 )-(5). The method 700 may allow measurements to be done in a few seconds.

[0069] The method 700 depicted in Fig. 7 may be further improved by activating and biasing the third optical module 612 to generate a third bias optical beam 632. The method 700 may further comprise generating the third bias optical beam 632 to illuminate the at least part of the silicon cell 604. Being illuminated by the third bias optical beam 632, a photosensitive region of the at least part of the silicon cell 604 is excited to generate charge carriers, which then recombine to emit a third bias photoluminescence signal 634b. The method 700 may further comprise a step of capturing the third bias photoluminescence signal 634b. The method 700 may further comprise a step of characterising the silicon cell 604 comprises analysing the third bias optical beam 632 and the third bias photoluminescence signal 634b. The third optical module 612 is biased to generate the third bias optical beam 632 for illuminating the at least part of the silicon cell 604. With a constant illumination intensity, the third bias optical beam 632 conditions the silicon cell 604 to a desired operation condition (e g. 1 sun, 2 suns) for measuring carrier lifetime using the second modulated optical beam 630.

[0070] Figs. 8(a)-8(f) depict images of a perovskite sample generated using the method 300 based on the first embodiment 200 depicted in Fig. 2, with the modulated optical beam 210 having a modulation frequency of 400kHz and an exposure time of 2ms of the perovskite sample being illuminated by the modulated optical beam 210, comprising photoluminescence images, carrier lifetime images and phasor plot etc. In this specific example, the composition of the perovskite sample comprises Cso -i8FAo.82Pb(l, Br)s and the perovskite sample has a bandgap of 1 .68 eV. Fig. 8(a) depicts an image of the perovskite sample generated based on a spatially distributed intensity of the captured modulated photoluminescence signal 226, with PL intensity (normalised, the maximum PL counts that can be registered by the camera is treated as 1 or the saturation of camera capacity is 1 ) range from 0.25 to 0.44, and from 0.44 to 0.62. Such data may be helpful in assessing uniformity of the perovskite sample. For example, Fig. 8(a) shows that the perovskite sample being measured has a relatively good level of uniformity, although there are tiny spots that has high PL intensity, as a majority area of the image shows a PL intensity around the middle of the range of 0.25 to 0.44. Fig. 8(b) depicts a result of phase imaging of the perovskite sample based on the captured modulated photoluminescence signal 226, which may be used to deduce effective charge carrier lifetime of the perovskite sample. Fig. 8(b) shows that the detected phase changes range from 10.2 to 11 .3, and from 11 .3 to 12.5 degrees. Fig. 8(c) depicts a spatially distributed lifetime of the perovskite sample deduced based on phase imaging of Fig. 8(b), according to equation (3). As shown in Fig. 8(c), some areas 800 of the perovskite sample being measured has a phase lifetime in the range from 79.6ns to 87.9 ns; while some areas 802 are observed to have a phase lifetime in the range from71.2 ns to 79.6 ns. Such information may also be helpful in characterising the perovskite sample such as for evaluating non-uniform ity. Fig. 8(d) depicts a result of modulation imaging of the perovskite sample showing modulation index obtained (in the range from 0.944 to 0.962, and from 0.962 to 0.979), which may also be used to deduce effective charge carrier lifetime of the perovskite sample. Fig. 8(e) depicts a spatially distributed lifetime of the perovskite sample deduced based on modulation index of Fig. 8(d), according to equation (5). As shown in Fig. 8(e), the perovskite sample generally has a modulation lifetime in the range from 82.7 ns to 139.0 ns, wherein a large continuous area 804 having a modulation lifetime in the range from 110.8 ns to 139.0 ns, near 110.8 ns. Figs. 8(c) and 8(e) show a similar lifetime measuring results to each other, which may suggest that the perovskite sample shows a single-exponential decay.

[0071] Fig. 8(f) depicts a phasor plot which provides 2D graphical view of the lifetime distribution. The phasor plot reveals the sample’s decay characteristics (e g. singleexponential or multi-exponential decay) and visualizes the heterogeneity of material characteristics of the perovskite material. In the phasor plot, x axis is Mcos p, y axis is Msin p. A single point on the phasor plot represents a specific combination of phase lifetime and modulation lifetime. When the phase lifetime equals the modulation lifetime, the point lies directly on the semicircle of the phasor plot, indicating a singleexponential decay of luminescence. In contrast, if the luminescence decay is multiexponential, the points will fall within the semicircle. The cloud of points in the phasor plot reflects the heterogeneity in carrier lifetime characteristics of all pixels in the image. Differences between the phase lifetime and modulation lifetime may highlight correlations between lifetime and microstructural features, such as various defect types (e.g., grain boundaries, phase segregation, process-induced defects), degradation patterns, and processing methods. Fig. 8(f) shows that a majority portion of the lifetime distribution points fall on or near to the semicircle of the phasor plot, indicating single-exponential decay. This corroborate the results that the lifetime results of Figs. 8(c) and 8(e) are similar. In summary, by obtaining the above discussed images, the perovskite may be characterised from different angles. Overall, Figs. 8(a) to 8(f), demonstrate low contrast, small differences between the longest lifetime and shortest lifetime, small and circular clouds in the phasor plot are on or near to the semicircle, which all show very good uniformity of the perovskite material.

[0072] It should be apparent that the same measurement conditions as illustrated in Figs 8(a) to 8(f) may not necessarily apply to all Cso.i8FAo 82Pb(l, Br)3 perovskites. The specific conditions would depend on the individual sample and the measurement system being used.

[0073] Figs. 9(a)-9(f) depict images of a perovskite cell in a perovskite / silicon tandem device sample generated using the method 700 based on the fourth embodiment 600 depicted in Fig. 6(a), with the first modulated optical beam 626 having a modulation frequency of 400kHz and an exposure time of 50ms of the perovskite cell being illuminated by the first modulated optical beam 626, comprising photoluminescence images, carrier lifetime images and phasor plot etc. Fig. 9(a) depicts an image of the perovskite cell generated based on a spatially distributed intensity of the captured first modulated photoluminescence signal 628, with PL intensity (normalised, the maximum PL counts that can be registered by the camera is treated as 1 or the saturation of camera capacity is 1) range from 0.34 to 0.52, and from 0.52 to 0.70. Fig. 9(a) shows a generally continuous intensity distribution suggesting some degree of uniformity, but it is not perfectly uniform, otherwise, there should be no contrast at all and the PL intensity should be one single value. Fig. 9(b) depicts a result of phase imaging of the perovskite cell based on the captured first modulated photoluminescence signal 628, which may be used to deduce effective charge carrier lifetime of the perovskite cell. In Fig. 9(b), the detected phase changes range from 10.7 to 16.4 degrees, and from 16.4 to 22.2 degrees. Fig. 9(c) depicts a spatially distributed lifetime of the perovskite cell deduced based on phase imaging of Fig. 9(b), according to equation (3). As shown in Fig. 9(c), a majority area 900 of the perovskite cell being measured has a phase lifetime in a range from 118.7 ns to 162.3 ns; while some areas 902 has a phase lifetime in a range from 75.2 ns to 118.7ns. Fig. 9(d) depicts a result of modulation imaging of the perovskite cell showing modulation index obtained (in the range from 0.896 to 0.943, and from 0.943 to 0.989), which may also be used to deduce effective charge carrier lifetime of the perovskite cell. Fig. 9(e) depicts a spatially distributed lifetime of the perovskite cell deduced based on modulation index of Fig. 9(d), according to equation (5). As shown in Fig. 9(e), a majority area 904 of the perovskite cell has a modulation lifetime in the range from 127.6 ns to 196.5 ns, with some other areas 906 having a modulation lifetime in the range of 58.7 ns to 127.6 ns. Figs. 9(c) and 9(e) show similar lifetime results to each other, which suggests that the perovskite cell being measured show single-exponential decay. This is also consistent with the results shown in phasor plot of Fig. 9(f), which demonstrates that a majority of the cloud of lifetime points lies directly on / along the semicircle of the phasor plot, indicating a single-exponential decay of luminescence. These results show that, in this perovskite / silicon tandem device sample, the perovskite top cells conformably cover the surface of the silicon bottom cells, with no pyramid tips of silicon visible.

[0074] Figs. 10(a)-10(e) depicts images of a perovskite cell in another perovskite / silicon tandem device sample generated using the method 700 based on the fourth embodiment 600 depicted in Fig. 6(a), with the first modulated optical beam 626 having a modulation frequency of 400kHz, and an exposure time of 600ms of the perovskite cell being illuminated by the first modulated optical beam 626, comprising photoluminescence images and carrier lifetime images etc. Fig. 10(a) depicts an image of the perovskite cell generated based on a spatially distributed intensity of the captured first modulated photoluminescence signal 628, with PL intensity (normalised, the maximum PL counts that can be registered by the camera is treated as 1 or the saturation of camera capacity is 1 ) range from 0.10 to 0.54, and from 0.54 to 0.97. Multiple individual spots 1000 with a PL intensity near the lower end of 0.10, some areas 1002 of the perovskite cell have a PL intensity in the middle of the range, i.e. around 0.54, while some areas 1004 are shown to have a PL intensity of near the upper end, i.e. 0.97. Such data may be helpful in assessing uniformity of the perovskite cell. Particularly, the spots 1000 demonstrates tips of silicon pyramids under the perovskite cell. In the perovskite / silicon tandem device sample, the surface of bottom silicon cell has a random pyramids texture with the spots 1000 serving as tips of the pyramids. Such pyramids increase light absorption, which creates challenges in depositing uniform perovskite cells on top of the silicon surface. This shows that, in some areas, the perovskite film may only cover the valleys between the pyramids so that the tips 1000 of pyramids are exposed, i.e. there is no perovskite film coving the pyramid tips 1000. Thus, there is no emitted luminescence in these regions, so they appear dark in the Photoluminescence images. Fig. 10(b) depicts a result of phase imaging of the perovskite cell based on the captured first modulated photoluminescence signal 628, which may be used to deduce effective charge carrier lifetime of the perovskite cell. Fig. 10(b) shows that the detected phase changes range from 0.1 to 14.1 degrees, and from 14.1 to 28.0 degrees. Fig. 10(c) depicts a spatially distributed lifetime of the perovskite cell deduced based on phase imaging of Fig. 10(b), according to equation (3). As shown in Fig. 10(c), a majority area 1006 of the perovskite cell being measured has a phase lifetime in the middle of the general range of 0 to 199.9 ns, i.e. around 99.9 ns; while some smaller areas 1008 have a phase lifetime around the lower end of the range of 0 to 99.9 ns. Fig. 10(d) depicts a result of modulation imaging of the perovskite cell showing modulation index obtained (in the range from 0.1 to 11.5, and from 11.5 to 23.0), which may also be used to deduce effective charge carrier lifetime of the perovskite cell. Fig. 10(e) depicts a spatially distributed lifetime of the perovskite cell deduced based on modulation index of Fig. 10(d), according to equation (5). As shown in Fig. 10(e), areas 1008 of the perovskite cell have a modulation lifetime near the upper end of range from 493.4 ns to 986.9 ns, while areas 1010 having a modulation lifetime near the lower end of range from 0 to 493.4 ns. Figs. 10(c) and 10(e) show different lifetime results to each other, which suggests that the perovskite cell show multi-exponential decay.

[0075] The exposure time impacts the PL intensity: the longer the exposure time, the higher the PL intensity. The exposure time is chosen so that the normalized PL intensity falls within the median range of 0 to 1 , preferably in a range from 0 to 0.61 . For a sinusoidal modulated signal, the registered PL intensity represents the integrated value of the sinusoidal curve. By controlling the highest intensity to remain below 0.61 , it ensures that the peak of the sinusoidal curve does not exceed 1 avoiding the risk of saturating the detector or camera. Generally, the exposure time may be selected from a range 1 ms to 2 seconds; preferably, 10ms to 1000ms, preferably 50ms to 600ms, more preferably 100ms to 500ms, even more preferably 200ms to 400ms, or particular exposure time within any of these exposure time ranges. With the short exposure time, measurements are allowed to be completed within seconds, making this method suitable for production monitoring.

[0076] With the use of differently modulated optical beams to excite different materials of the semiconductor device, effective responses from materials of different lifetime scales and emission wavelengths are separated. Thus, the present invention is applicable for probing materials / devices when more than two types of optoelectronic materials / devices are present (e.g. probing perovskite sub-cells and Si sub-cells in a perovskite / Si tandem devices). By providing a rapid, contactless metrology technique, the present invention can provide localized area or spatially resolved (imaging) characterization of the semiconductor devices for assessing and monitoring of their fabrication process and understanding material and device properties, both in industrial large scale and laboratory scale. This is particularly important since the advantage of perovskite-based semiconductor devices (such as solar cells) being suitable to be integrated with silicon substrate / cell into a tandem device for high efficiency and energy output has been constrained. Similar to the embodiments for perovskite-based semiconductor device (e.g. Fig. 2), this proposed solution is applicable to both non-metallized and metallized tandem samples at different stages. It not only avoids the need of preparing separate sub-cell test samples, but also measures the performance of Si sub-cells in a tandem configuration more accurately. In addition to perovskite / Si tandem devices, similar technique can be applied to other tandem devices as long as the modulation frequencies and responses from sub-cells can be effectively separated.

[0077] While for Fig. 1 , one controlling module is described for controlling the various modules, it is envisaged that more controlling modules may be used for controlling different modules. It is also envisaged that various computing devices may function as a controlling module such as laptop, desktop, smartphone, embedded system etc. While there are multiple modules described, it is envisaged that different functional modules of a single apparatus or multiple apparatuses may be mixed and grouped together and treated as one module. For example, the data processing module 108 and the controlling module 102 may be different functions of a single embedded system. As another example, signal capturing function and data processing function may be two functions of one single device and thus such single device can be treated as both the signal capturing module 110 and data processing module 108. As a further example, the illumination module 106 may be integrated with modulation function so that there may not be a standalone modulation module, or the modulation function may be integrated in the controlling module. It is also envisaged the different modules may be provided separately, and assembled onsite for measuring.

[0078] It is envisaged that the whole system of the present invention may not be a singleassembled apparatus, and different functional modules that work together to realise the system may come from different apparatus. For example, the illumination module 106 and the signal capturing module 110 may be controlled by a controlling module 102 which locate remotely to the illumination module 106 and the signal capturing module 110.

[0079] While the steps of the above methods are described one after another and the blocks corresponding to the steps of the methods depicted in Figs. 3 and 7 are connected by arrows, it is envisaged that the steps of the methods may be performed in other orders. For example, the step 704 of exciting at least part of the silicon cell 604 with the second modulated optical beam 630 may be performed before the step 702 of exciting at least part of the perovskite cell 606. It is also envisaged that the step 702 and the step 704 may be performed at the same time as the modulation frequency and emission wavelength of different optoelectronic materials (e.g. perovskite and Si) are different so that response of the sub-cells can be separated. It is further envisaged that the step 706 of capturing the first modulated photoluminescence signal 628 and the second modulated photoluminescence signal 634a may be split into different steps. It is further envisaged that the perovskite cell 606 and the silicon cell 604 may be performed at the same time or at different time.

[0080] While Figs. 2 and 4 depict that the solutions are measuring the perovskite cell of the semiconductor device, it is envisaged that the solutions are also applicable to a semiconductor device the entire body of which is a perovskite material. While Figs. 6(a) and 6(b) depict that the silicon cell 604 and the perovskite cell 606 are in a tandem configuration, it is envisaged that the semiconductor device to be probed may have other structure or configuration, such as the semiconductor device may be a device the whole body of which is based on the same material, or with two or more cells with a tandem configuration or a parallel configuration. While Figs. 6(a) and 6(b) depict that the semiconductor device 602 comprises the perovskite cell 606 and the silicon cell 604, it is envisaged that the semiconductor device to be probed using the third embodiment 500 may comprise two cells with other different semiconductor materials, for example, one cell may be based on any material selected from a group comprising perovskite, silicon, Cadmium Telluride (CdTe), germanium (Ge), Copper Indium Gallium Selenide (CIGS), Copper Zinc Tin Sulfide (CZTS), indium phosphide (InP) gallium arsenide (GaAs) , gallium indium phosphide (GalnP) and other lll-V semiconductor materials etc., while another cell be based on any other material of the group. It is also envisaged that the semiconductor device may comprise more than two cells and at least two of the cells are based on semiconductor materials different from each other. Fig. 11 is a table illustrating some examples of semiconductor devices with multi-junction solar cells that the method of Fig. 7 may be used to characterise. As shown in Fig. 11 , a semiconductor device may comprise different layers of materials. For different material layers, the respective parameters (such as excitation wavelength, emission / detection wavelength, estimated carrier lifetime and estimated modulation frequency) are different. It is apparent that Fig. 11 is not exhaustive, and there may be other types of semiconductor devices with different structure that can be measured using the present invention.

[0081] While Fig. 6(b) depicts that the third optical module 612 is biased to generate the third bias optical beam 632 for illuminating the at least part of the silicon cell 604 for condition the silicon cell 604 to particular operation conditions, it is envisaged that the third bias optical beam 632 may also be used to condition the perovskite cell 606 to a particular operation conditions when the silicon cell 604 and the perovskite cell 606 are measured separately. It is also envisaged that there may be an optical module in addition to the third optical module 612 and such additional optical module functions the same as or similarly to the third optical module 612, so that the third optical module 612 and the additional optical module may be used to condition the silicon cell 604 and the perovskite cell 606 respectively.

[0082] Similarly, it is envisaged that the third embodiment 500 may be modified by adding one or more optical module for generating optical beams to condition the first semiconductor material 504 and / or the second semiconductor material 506. It is also envisaged that “first” and “second” are used to merely identify two parts from each other and does not serve to provide any meaning of the parts being identified, so that a part can be identified as a first part or a second part or the like and such identification per se does not limit the part.

[0083] While Figs. 8-10 describe actual results of characterising perovskite cell of a tandem semiconductor device by detecting phase / modulation changes using the method 700 based on the fourth embodiment 600, it is envisaged that the data processing methods (including equations (1 )-(5)) may be applied to charactering a perovskite material using the method 300 based on the first embodiment 200 or the second embodiment 400, and may yield similar images.

[0084] While it is described in the above, that some optical beams are modulated with a sinusoidally modulated illumination intensity, it is envisaged that the optical modules may be modulated to generate optical beams with functions other than sine wave, such as square wave, triangular wave, saw tooth wave and ramp wave etc.

[0085] It is envisaged that different light sources may be used to generate modulated optical beams, such as laser diode, LEDs etc. It is also envisaged that one illumination module may comprise one or more light sources, such as one or more laser diodes, or one or more LEDs.

[0086] It is envisaged that, when integrated with appropriate optical and electronic components and signal capturing modules, microscopic and wide field images can be generated, offering valuable spatially resolved information. With such alteration, the present invention is capable of being expanded with a microscopic configuration so as to investigate micro-structural characteristics or in a wide-field configuration so as to investigate large area device, particularly for industrial application.

[0087] While the embodiments show that excitation and luminescence filters are used, it is envisaged that such filters may not be used, such as a modulated laser beam may be directed to illuminate a semiconductor material without being filtered.

[0088] It is envisaged that the signal capturing module may comprise different detector and / or cameras for capturing the photoluminescence signals, subject to the nature of the signal to be captured. It is envisaged that a camera or detector may be selected from the group of frequency-domain fluorescence lifetime imaging (FD-FLIM) camera, short-wave infrared InGaAs camera, InGaAs detector, infrared detector and visible to near infrared detector etc.

[0089] While the third embodiment 500 and the fourth embodiment 600 both show two-layer structure of semiconductor devices, it is envisaged that there may be more layers, such as the three-layer example of “GalnP / GaAs / Ge” provided in Fig. 11 .

Claims

CLAIMS1 . A method for luminescence characterisation of a perovskite material, the method comprises: exciting at least part of the perovskite material with a modulated optical beam to emit a modulated photoluminescence signal, the modulated optical beam having a modulation frequency that is selected based on an estimated lifetime of the perovskite material to be characterised; capturing the emitted modulated photoluminescence signal; analysing a phase and / or modulation change between the modulated optical beam and the modulated photoluminescence signal for characterising the perovskite material.

2. The method according to claim 1 , wherein the modulation frequency of the modulated optical mean is between 150 kHz and 160 MHz, and / or wherein the emitted modulated photoluminescence signal has a wavelength of between 600 nm and 900 nm.

3. The method according to claim 1 or 2, wherein capturing the modulated photoluminescence signal comprises capturing one or more images of the perovskite material.

4. A system for luminescence characterisation of a perovskite material, the system comprises: an illumination module operable to generate an optical beam for exciting at least part of the perovskite material to emit a modulated photoluminescence signal, the modulated optical beam having a modulation frequency that is selected based on an estimated lifetime of the perovskite material to be characterised; a signal capturing module operable to capture the modulated photoluminescence signal; and a data processing module operable to analyse a phase and / or modulation change between the modulated optical beam and the modulated photoluminescence signal for characterising the perovskite material.

5. The system according to claim 4, wherein the modulation frequency of the modulated optical beam is between 150 kHz and 160 MHz, and / or wherein the emitted modulated photoluminescence signal has a wavelength of between 600 nm and 900 nm.

6. The system according to claim 4 or 5, wherein the signal capturing module comprises a frequency-domain fluorescence lifetime imaging camera.

7. A method for luminescence characterisation of a semiconductor device comprising a first semiconductor material and a second semiconductor material, the method comprises: exciting at least part of the first semiconductor material with a first modulated optical beam to emit a first modulated photoluminescence signal; exciting at least part of the second semiconductor material with a second modulated optical beam to emit a second modulated photoluminescence signal; capturing the emitted first modulated photoluminescence signal and the emitted second modulated photoluminescence signal for respectively characterising the first semiconductor material based on the first modulated optical beam and the emitted first modulated photoluminescence signal and the second semiconductor material based on the second modulated optical beam and the emitted second modulated photoluminescence signal, wherein the first modulated optical beam and the second modulated optical beam are modulated at different frequencies and / or have different excitation wavelengths.

8. The method according to claim 7, wherein capturing the emitted first modulated photoluminescence signal is performed after exciting the at least part of the first semiconductor material with the first modulated optical beam, but before exciting the at least part of the second semiconductor material with the second modulated optical beam.

9. The method according to claim 7 or 8, wherein an exposure time of the at least part of the first semiconductor material being illuminated by the first modulated optical beam is in a range from 1 ms to 2 seconds.

10. The method according to any of claims 7 to 9, wherein the first semiconductor material and the second semiconductor material are in a tandem configuration and characterising the first semiconductor material and the second semiconductor material comprises determining a distribution of the first semiconductor material over the second semiconductor material.11 . The method according to any of claims 7 or 10, further comprising: exciting the at least part of the second semiconductor material to emit a third bias photoluminescence signal; capturing the third bias photoluminescence signal for characterising the second semiconductor material based on the third bias optical beam and the third bias photoluminescence signal.

12. The method according to claim any of claims 7 to 11 , wherein: capturing the first modulated photoluminescence signal comprises capturing one or more images of the first semiconductor material, and / or capturing the second modulated photoluminescence signal comprises capturing one or more images of the second semiconductor material.

13. The method according to any of claims 7 to 12, wherein the first modulated optical beam has a modulation frequency of between 150 kHz and 160 MHz, and / or wherein the first modulated photoluminescence signal is captured at a wavelength of between 600 nm and 900 nm, and / or wherein the second modulated optical beam has a modulation frequency of 100Hz to 100kHz.

14. The method according to any of claims 7 to 13, further comprising:analysing a phase and / or modulation change between the first modulated photoluminescence signal and the first optical beam for characterising the first semiconductor material, and / or analysing a phase and / or modulation change between the second modulated photoluminescence signal and the second modulated optical beam for characterising the second semiconductor material.

15. A system for luminescence characterisation of a semiconductor device comprising a first semiconductor material and a second semiconductor material, the system comprises: a first illumination module operable to generate a first modulated optical beam for exciting at least part of the first semiconductor material to emit a first modulated photoluminescence signal; a second illumination module operable to generate a second modulated optical beam for exciting at least part of the second semiconductor material to emit a second modulated photoluminescence signal; a first signal capturing module operable to capture the first modulated photoluminescence signal; a second signal capturing module operable to capture the second modulated photoluminescence signal; and a data processing module operable to analyse the first modulated optical beam and the first modulated photoluminescence signal for characterising the first semiconductor material, and to analyse the second modulated optical beam and the second modulated photoluminescence signal for characterising the second semiconductor material, wherein the first modulated optical beam and the second modulated optical beam are modulated at different frequencies and / or have different excitation wavelengths.

16. The system according to claim 15, wherein the first semiconductor material and the second semiconductor material are in a tandem configuration and the data processing module is operable to characterise the first semiconductor material andthe second semiconductor material to determine a distribution of the first semiconductor material over the second semiconductor material.

17. The system according to claim 15 or 16, further comprises a third illumination module operable to be biased to generate a third bias optical beam for exciting the at least part of the second semiconductor material to emit a third bias photoluminescence signal, wherein the second signal capturing module is operable to capture the third bias photoluminescence signal, wherein the data processing module is operable to analyse the second modulated optical beam, the second modulated photoluminescence signal, the third bias optical beam and the third bias photoluminescence signal to characterise the second semiconductor material.

18. The system according to any of claims 15 to 17, wherein the first modulated optical beam has a modulation frequency of between 150 kHz to 160 MHz, and / or wherein the first signal capturing module is sensitive in a wavelength range from 600 nm and 900nm, and / or wherein the second modulated optical beam has a modulation frequency of 100Hz to 100kHz.

19. The system according to any of claims 15 to 18, wherein the first signal capturing module comprises a frequency-domain fluorescence lifetime imaging camera.

20. The system according to any of claims 15 to 19, wherein the second signal capturing module comprises a frequency-domain fluorescence lifetime imaging camera or a short-wave infrared InGaAs camera.

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