System for the measurement of polarization-induced charge transfer in optoelectronic and photoelectrochemical devices

Abstract

The single set-up measurement of time-resolved photovoltage (TPV) and time- resolved photocurrent (TPC) of optoelectronic and photoelectrochemical devices is achieved by an automated system that enables charge generation, and analysis of extraction and recombination dynamics of the devices at interfacial and bulk regions at different measurement conditions. The system comprises of sample holder and controllers section (1), light sources and controllers section (2), data acquisition unit (3), electronic switches (50), which are controlled and monitored by a data processor (40). The system provides for optical perturbation wavelengths, pulse- width, and light-soaking, in addition to different electric field polarizations, magnetic field polarizations and various temperature regimes for the measurement of photovoltage and photocurrent over time. Examples of optoelectronic and photoelectrochemical devices include devices for water splitting, carbon dioxide reduction, nitrogen reduction, light emitting diodes, photodetectors, and solar cells.

Description

[0001] DESCRIPTION

[0002] Title of the invention: System for the measurement of polarization-induced charge transfer in optoelectronic and photoelectrochemical devices

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to a fully automated system for the measurement of polarization-induced charge transfer, more particularly, the measurement of time- resolved photovoltage (TPV) and time-resolved photocurrent (TPC) of optoelectronic and photoelectrochemical devices with two-electrode and three- electrode configurations.

[0005] BACKGROUND OF THE INVENTION

[0006] Charge extraction and recombination dynamics are fundamental processes in optoelectronic and photoelectrochemical devices, governing their efficiency and performance. While charge extraction is a process by which photogenerated charges such as electrons and holes are swept away from their site of generation to electrodes or other charge-collecting interfaces, where they can participate in desired functions such as current generation or light emission, recombination is a process by which photogenerated electrons and holes lose their energy, typically through the emission of light (photoluminescence) or heat. Recombination is an undesirable process in most optoelectronic and photoelectrochemical devices as it reduces the number of charges available for desired applications. The interplay between charge extraction and recombination determines the overall efficiency of a device. Ideally, devices are designed to maximize charge extraction and minimize recombination. This can be achieved through various strategies such as using materials with high charge carrier mobilities and low defect densities to facilitate efficient transport of charges, and optimizing the interface between different materials in the device to minimize energy barriers for charge transport and suppress recombination.

[0007] Understanding and controlling charge extraction and recombination dynamics is crucial for the development of high-performance optoelectronic and photoelectrochemical devices. Various experimental techniques are used to study processes wherein decay of current, voltage and photoluminescence is measured over time. These include transient photovoltage and photocurrent spectroscopy wherein the change in the voltage and current following a short pulse of light is monitored to study recombination and charge extraction dynamics, and electrochemical impedance spectroscopy wherein the impedance of the device is analyzed to understand the kinetics of charge transport and recombination.

[0008] By studying charge extraction and recombination dynamics, researchers can gain valuable insights into the operation of optoelectronic and photoelectrochemical devices and develop strategies to improve their efficiency and performance. In solar cells, charge extraction involves the separation of photogenerated electrons and holes in the light-absorbing layer and their transport to the electrodes where they generate current. Recombination within the device reduces the number of charges that reach the electrodes thus limiting the efficiency of the cell. In Light Emitting Diodes (LEDs), charge recombination leads to the emission of light. The efficiency of LEDs depends on the rate of radiative recombination which produces light compared to non-radiative recombination which produces heat. In photoelectrochemical cells, photogenerated charges are used to drive chemical reactions at the electrode surfaces. The efficiency of these cells depends on the balance between charge extraction to the electrodes and recombination within the device. By controlling charge extraction and recombination dynamics, researchers can develop new and improved optoelectronic and photoelectrochemical devices with higher efficiencies resulting in a wider range of applications.

[0009] The characterization of photovoltaic devices by means of photovoltage and photocurrent transients gives information on several important properties of the devices, such as their charge carrier lifetime and transport rate. In these techniques, the device is perturbed by a modulated light and the photovoltage and photocurrent are recorded in the time or frequency domain, from which important information about the device can be obtained. An advantage is that such measurements can be done on devices, under diverse conditions that are comparable to practical operating conditions. In the quest to understand defect states and carrier recombination processes in photovoltaic solar cells, researchers have employed various techniques, including intensity-modulated photovoltage and photocurrent spectroscopy, and electrochemical impedance spectroscopy. Frequency domain methods such as these demand a solid theoretical foundation and involve intricate data management and analysis. Conversely, time resolved photoelectric and photoelectrochemical measurements are time-domain methods offering simpler measurement results and data analysis. However, the latter requires constant parameter adjustments, leading to repetitive and time-consuming tasks that can reduce the efficiency of technical staff during data acquisition. The development of methods for analyzing defect states and carrier recombination processes in photovoltaic solar cells is crucial for progress in the field.

[0010] CN217305310U discloses a photovoltaic device testing arrangement for transient state photocurrent and photovoltage. It comprises a testing clamp, displacement platform, switching module, signal module, pulse laser, sunlight simulator, and camera. The system allows testing with adjustable light spot position, controlled switching, and signal amplification through computer software, providing fast and user-friendly testing. However, its ability to analyze charge transport and recombination dynamics is limited when it comes to diverse conditions, temperature regimes, and polarization settings within the same step-up. CN114002484B discloses a transient photovoltage test sample assembly comprising a first clamping plate with a groove for holding a sample electrode, a second clamping plate, and an electrode plate with magnetic materials in between. The magnetic material stabilizes the electrode, preventing displacement during measurement, and shields against external magnetic interference. The assembly allows exposure of the sample electrode for in situ reactions, providing insights into transient photovoltage during these reactions. The design enhances accuracy by maintaining stability and minimizing external interference.

[0011] CN114884465 A discloses a transient photovoltaic testing apparatus for solar cells. It combines a steady-state light source (LED) and a transient pulse light source (semiconductor laser) to stimulate carrier dynamics. The apparatus includes a stabilized voltage power supply, a light source system, and a measuring circuit module. The LED provides stable irradiation, while the semiconductor laser performs transient excitation after stable photovoltage generation. The measuring circuit detects changes in photovoltage and photocurrent over time, allowing for the analysis of carrier dynamics and ion migration under different illumination conditions.

[0012] CN216565074U discloses an adjustable transient photoelectric measurement system for studying the behavior of photoelectric devices such as solar cells. It has various modules for adjusting illumination, laser pulses, voltage bias, etc. The system can quickly and automatically measure how these devices respond to different conditions, helping analyze their charge transport and recombination properties. It is designed to be efficient, saving time and effort in measurement and data analysis through its integrated structure and automation features.

[0013] CN110880913A discloses a dynamic testing device for a photovoltaic cell. The device includes a clamp to hold the solar cell, a steady light source for constant light, a pulse light source for quick bursts of light, an oscilloscope to measure voltage changes, and a rheostat to control resistance. The steady light source produces a stable voltage signal, while the pulse light source generates a quick voltage signal. The oscilloscope records these signals in real-time. The rheostat adjusts resistance to simulate different load conditions for the solar cell. This device enables testing of solar cells under real working conditions, aiding research on their dynamic performance.

[0014] CN108055004B discloses a photovoltaic solar cell transient state photocurrent full - automatic test system and test method. The system includes fixtures to hold the cells, a stable light source for steady-state signals, a pulse light source for transient signals, a switch to control light exposure, a unit to adjust light intensity, and a computer for real-time data acquisition and analysis. It is useful in the field of photovoltaic semiconductors for efficiently gathering data during different operating conditions. However, none of the systems cited above, stimulate or analyze carrier dynamics (charge transport) and recombination dynamics with diverse conditional aspects such as varying optical perturbation wavelengths, pulse-widths, and light-soaking. These do not disclose the use of a single system that can be utilized to measure electric field polarization, magnetic field polarization, and temperature dependent photovoltage and photocurrent data over time.

[0015] To address the aforementioned problems, the inventors of the present invention have developed a system for the measurement of charge generation and extraction dynamics and recombination properties of optoelectronic and photoelectrochemical devices with varying optical perturbation wavelengths, pulse-widths, and lightsoaking. Also, said system provides for different electric field polarizations, magnetic field polarizations, and various temperature regimes for the measurement of photovoltage and photocurrent over time.

[0016] OBJECT OF THE INVENTION

[0017] The main object of the present invention is to provide a system for analyzing charge generation and extraction dynamics, recombination properties, and distribution of trap states of optoelectronic and photoelectrochemical devices through the measurement of TPV and TPC, with or without electric polarization.

[0018] Another object of the invention is to provide a system for analyzing charge generation and extraction dynamics, recombination properties, and distribution of trap states of optoelectronic and photoelectrochemical devices through the measurement of TPV and TPC, with or without magnetic polarization.

[0019] Yet another object of the invention is to provide a system for analyzing charge generation and extraction dynamics, recombination properties, and distribution of trap states of optoelectronic and photoelectrochemical devices through the measurement of TPV and TPC, at different temperature regimes.

[0020] Still yet another object of the invention is to provide a system for analyzing charge generation and extraction dynamics, recombination properties, and distribution of trap states of optoelectronic and photoelectrochemical devices with two electrodes or three electrodes, with or without electric or magnetic polarization at various temperature regimes.

[0021] Further object of the invention is to provide a system for analyzing charge generation and extraction dynamics, recombination properties, and distribution of trap states of photovoltaic systems, with or without electric or magnetic polarization at various temperature regimes.

[0022] Further yet another object of the invention is to provide a system for analyzing charge generation and extraction dynamics, recombination properties, and distribution of trap states through the measurement of TPV and TPC, in different devices used for water splitting, carbon dioxide reduction, and nitrogen reduction, as well as light emitting diodes, photodetectors and solar cells. Still another object of the invention is to provide a system for analyzing charge generation and extraction dynamics, recombination properties, and distribution of trap states through the measurement of TPV and TPC, both at the interfaces and bulk of the devices, from short-circuit to open-circuit conditions by sweeping the applied bias voltage

[0023] Still yet another object of the invention is to provide a system for analyzing charge generation and extraction dynamics, recombination properties, and distribution of trap states through the measurement of TPV and TPC, under various steady-state and operating conditions.

[0024] SUMMARY OF THE INVENTION

[0025] The present invention deals with a system for assessing charge extraction and recombination dynamics in optoelectronic and photoelectrochemical devices. Said system comprises features for the measurement of charge extraction and recombination dynamics of said device at interfacial and bulk regions under different background illumination intensities, optical perturbation wavelengths, and pulse-widths. Said system also provides for light-soaking, electric and magnetic field polarizations and variable temperature regimes. Said system comprises designated sample holders for conducting measurements at room temperature with or without electric or magnetic polarization, and also for the measurement of variable temperature TPV and TPC. Said system is fully automated using a customized program created using Lab View software.

[0026] Said system is used for the measurement of TPV and TPC in optoelectronic and photoelectrochemical devices. Said system comprises a plurality of electrode configurations, for conducting experiments in electric fields, magnetic fields, or a combination thereof, whereby measurements can be performed across various temperature ranges, spanning from liquid nitrogen temperature to room temperature and above. Said system is fully automated and offers versatility via different configurations and conditions.

[0027] BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The summary of the present invention, as well as the brief description, are better understood when read in conjunction with the accompanying drawings that illustrate one or more possible embodiments of the present invention, of which: Figure l is a schematic representation of the system of the present invention for the assessment of polarization-induced charge transfer in optoelectronic and photoelectrochemical devices by measuring TPV and TPC under electric polarization and magnetic polarizations;

[0029] Figure 2 illustrates a room temperature sample holder for the measurement of TPV and TPC under electric polarization and magnetic polarization;

[0030] Figure 3 illustrates a variable temperature sample holder for the measurement of TPV and TPC under electric polarization; Figure 4 illustrates a photoelectrochemical sample holder for the measurement of TPV and TPC at different potentials and magnetic field intensities during the photoelectrochemical reactions;

[0031] Figure 5 illustrates a display of the Lab View software wherein the measurement parameters are set and data acquisition is performed;

[0032] Figure 6 illustrates the data collected by the sourcemeter displaying both larger transient photovoltage and smaller transient photovoltage measurements;

[0033] Figure 7 illustrates light-intensity dependent transient photovoltage measurements, recorded by an oscilloscope;

[0034] Figure 8 illustrates a transient photocurrent decay at different illumination intensities;

[0035] Figure 9 illustrates a transient photovoltage decay under different electric polarizations;

[0036] Figure 10 shows the magnetic field polarization-dependent transient photovoltage measurements; and

[0037] Figure 11 shows the temperature-dependent transient photovoltage measurements.

[0038] DETAILED DESCRIPTION OF THE INVENTION

[0039] The present invention relates to a system for assessing the dynamics of charge generation and extraction, as well as the recombination properties, in optoelectronic devices and photoelectrochemical devices. These devices may possess multielectrode configurations, and may or may not have electric polarization or magnetic polarization. The assessment can be conducted across various temperature regimes. The time-resolved system of the present invention can help study the transient photovoltage and photocurrent decay measurements in any optoelectronic device or photoelectrochemical device such as but not limited to devices for water splitting, carbon dioxide reduction, nitrogen reduction, light emitting diodes, photodetectors, and solar cells. The photovoltage and photocurrent decay provide information about the charge transfer dynamics including carrier recombination, transport, carrier extraction, and distribution of trap states.

[0040] The system of the present invention for conducting a variety of TPV and TPC measurements as shown in Figure 1, comprises of a sample holder and controllers section (1), light sources and controllers section (2), data acquisition unit (3), electronic switches (50), and a computer with Lab View software (40), wherein said sample holder and controllers section (1) comprises a sample holder (10), a electrochemical workstation (11), a temperature controller (12), an electromagnet controller (13), pumps (14), a liquid nitrogen tank (15), and programmable DC power supply (16); said light sources and controllers section (2) comprises light sources including white LED (20), pulsed LED or LASER (21), programmable DC power supply (22), function generator (23), and power supply for the fan (24) of said white LED (20); and said data acquisition unit (3) comprises an oscilloscope (30), sourcemeter (31), and data acquisition system (DAQ) (32). Said system is interconnected using electronic switches (50). The components of said system of the present invention are controlled by a computer with Lab View software (40). The customized program created using Lab View software controls and monitors the power supply used for the regulation of white bias illumination, sourcemeter (31), function generator (23), oscilloscope (30), data acquisition (DAQ) system

[0041] (32), and power supply (22).

[0042] Said light sources (20, 21) and sample holder (10) are placed in a Faraday cage (4) to provide electromagnetic shielding. Said sample holder (10) is used for performing a variety of TPV and TPC measurements with or without electric and magnetic polarization. The device under test (DUT) is placed in the sample holder. Different types of samples for which TPV and TPC measurements are to be performed, are placed in the sample holder, and subjected to light sources such as white LED (20), and pulsed LED or LASER (21) with the focus being on the central part of the DUT. The temperature of the device is varied using a temperature controller (12). A single-pole electromagnet (130) controlled by an electromagnet controller (13) is used for conducting measurements with magnetic polarization. The photoelectrochemical reactions are measured with an electrochemical workstation (11) with the terminals being connected to said data acquisition unit (3) through said electronic switches (50).

[0043] For data acquisition, an appropriate sample holder is selected. For the measurement of TPV and TPC at room temperature, a room temperature sample holder (1001) shown in Figure 2 is used. For temperature-dependent measurement of TPV and TPC, the sample is placed in a variable temperature sample holder (1002) shown in Figure 3, and the initial temperature and the temperature sweep range are fixed. For the measurement of TPV and TPC in photoelectrochemical reactions, a photoelectrochemical sample holder (1003) shown in Figure 4, is used.

[0044] According to an embodiment of the present invention, a sample holder (1001) shown in Figure 2 is used for conducting room temperature transient photovoltage and photocurrent measurements with or without electric and magnetic polarization. Said sample holder (1001) comprises a plurality of micromanipulators (10012, 10013, 10014, and 10015) shown in black color in Figure 2, which are attached to a non-magnetic metallic plate (10011). Said metallic plate (10011) is held vertically through hinges (10016) that are attached to a dual -rod post having a magnetic base. Said metallic plate (10011) may be an aluminum plate which further comprises a circular section (10017) at the center, wherein the DUT is placed. Said DUT is an optoelectronic sample which can be in the form of a thin film or a single crystal. Samples of dimension measuring from 4 x 4 mm2upto 4 x 4 cm2are placed on the circular section. Said light sources (20, 21) are focused on the central part of the plate on which said DUT is placed. An ultrafast silicon photodiode (10018) is used to test or calibrate said system.

[0045] Two of the micromanipulators (10012 and 10013), are connected to the positive electrode (5011) of the system, and the remaining pair of micromanipulators (10014 and 10015) are connected to the negative electrode (5021) of the system. The micromanipulators (10012 and 10014) serve the purpose of electrically polarizing the DUT (10018) when necessary, while the other micromanipulators (10013 and 10015) are used for the measurement of the signal across the DUT. The positive electrode (5011) and negative electrode (5021) connected to the micromanipulators at one end, are subsequently connected to said data acquisition unit (3) via electronic switches (50).

[0046] A single-pole electromagnet (130) controlled by an electromagnet controller (13) is utilized for the measurement of TPV and TPC with magnetic polarization. The magnet is placed in close proximity to the sample holder (1001). The two connections (1301 and 1302) of the magnetic pole (130) are connected to the terminals (131 and 132) of the electromagnet controller (13).

[0047] According to an embodiment of the present invention, as shown in Figure 3, the variable temperature sample holder (1002) for the measurement of TPV and TPC, is a liquid nitrogen-cooled cryostat (10020), and the DUT is placed in said variable temperature sample holder (1002). The temperature of the device is varied using a temperature controller (12). The vacuum inside the cryostat is maintained through a turbomolecular pump (141) and a rotary pump (142). The liquid nitrogen stored inside a liquid nitrogen container (15) is circulated inside the cryostat (10020) for cooling. The light sources white LED (20) and pulsed LED or LASER (21) are focused onto the device placed in the cryostat (10020) through a quartz window (10024). The positive electrode (10022) and negative electrode (10023) of the DUT are connected to the data acquisition unit (3) through the terminals (5011 and 5021) of the electronic switches (50). To electrically polarize the DUT, said programmable DC power supply (16) is connected to the electrodes of the DUT.

[0048] According to an embodiment of the present invention, the photoelectrochemical sample holder (1003) shown in Figure 4 comprises of a cell (10034), and three electrodes - Reference electrode (RE) (10035), Working electrode (WE) (10036), and Counter electrode (CE) (10037), wherein the DUT is placed in said cell (10034), and said electrodes (10035, 10036, and 10037) are dipped in an electrolyte to conduct photoelectrochemical reactions. The DUT acts as the working electrode (WE), Ag / AgCl and other standard reference electrodes including calomel and SHE (standard hydrogen electrode) are used as the reference electrode (RE), and platinum, carbon, gold, nickel or similar electrodes are used as the counter electrode (CE). A single-pole electromagnet (130) is placed close to the cell to magnetically polarize the DUT. The single-pole electromagnet (130) is controlled with a magnetic controller (13). To conduct the photoelectrochemical reactions, the three terminals (111, 112, and 113) of an electrochemical workstation (11) are connected to the WE (10036), CE (10037), and RE (10035) respectively. To electrically polarize the DUT, said programmable DC power supply (16) is connected to the terminals of the DUT, and the terminals (5011 and 5021) are connected to said data acquisition unit (3) through said electronic switches (50). The transient photovoltage is measured between the RE (10035) and WE (10036). The front panel of the computer equipped with customized program created using Lab View software (40) is shown in Figure 5. Said software enables the control of all the instruments such as power supply for the regulation of white bias illumination through DC power supply (22), sourcemeter (31), function generator (23), oscilloscope (30), DAQ (32), and power supply for applying electrical bias either individually or synchronously. Said power supply section regulates the intensity of the bias illumination by regulating the voltage and current settings. The turn-on and turn-off time, and the intensity adjustment of the bias illumination can be done through the Lab View software. The measurement of voltage and current is controlled by varying the source mode at the sourcemeter (31). The resolution of the acquired signal is selected by changing the horizontal scale of the oscilloscope (30). The data acquisition in said oscilloscope (30) is initiated upon receiving a trigger pulse from said function generator (23). The trigger time is controllable through the program. The pulsed LED or LASER (21) operates in the burst mode, and the different parameters of the burst mode such as duty cycle, number of cycles, period, and frequency are adjustable. The attribute of the DC power supply (22) is incorporated in the program which is used for applying the electrical bias. The magnitude of the applied potential and time duration is controlled through the program. The provision for conducting temperature-dependent transient photovoltage and temperature-dependent transient photocurrent measurements are also incorporated in the program. The starting temperature, final temperature, and the temperature interval can be set customized program created using Lab View software. Once this information is fed to the software, the instrument automatically sweeps the temperature from the starting point and begins measurements at each temperature interval. The upper display panel displays the data such as shorter transients acquired from the oscilloscope (30), and the lower display panel displays the data such as larger transients acquired by the sourcemeter (31). Figure 6 depicts the data acquired by said sourcemeter (31) where both larger transient signals and shorter transient signals are displayed. The duty cycle of the pulsed LED or LASER (21) is set in such a way that only a single pulse is generated when the larger transient reaches a steady-state value. The shorter transient signal acquired in the oscilloscope (30) is shown in Figure 7, wherein the measurement has been made by varying the intensity of the background illumination. The falling edge of the data provides information regarding the recombination dynamics of the charge carriers in the material or device.

[0049] According to an example, for analyzing the charge transport and recombination properties at a particular steady-state condition, two types of light sources are used in the system. White LED (20) is used forbackground illumination, and pulsed LED or LASER (21) is used for optical perturbations. The light beam from the white LED (20) is focused through different focusing optics (60) onto the DUT. Said light sources (20, 21) are placed inside a Faraday cage (4). The illumination intensity of said light sources (20, 21) is calibrated using a standard silicon reference cell. The system of the present invention has the provision to interchange the pulsed LEDs and LASERs as per the required wavelength of the optical perturbation. The start time, stop time, and the intensity of the white LED (20) are controlled through a programmable DC power supply (22). For the cooling of the white LED (20), a power supply (24) is used to run its fan. The pulse width and intensity of the pulsed LED and LASER (21) are varied through the customized program created using Lab View software. The start time and stop time of the pulsed LED and LASER (21) are controlled as per the trigger pulse obtained from the function generator (23). Said function generator (23) and programmable DC power supply (22) are controlled by the customized program created using Lab View software.

[0050] Electronic switches (50) connect said sample holder (10), said data acquisition unit (3), and said programmable DC power supply (16) as shown in Figure 1. The primary purpose is to isolate the data acquisition unit (3) from the sample holder

[0051] (10) while applying electric polarization. The connection between said data acquisition unit (3) and the programmable DC power supply (16) can be toggled with the switches 501 and 502. The selection of TPV or TPC measurement is made using the switch (503). If it is TPV, the potentiometer (5034) is bypassed, and the data acquisition unit (3) directly obtains the voltage data from the DUT. Alternately, if the measurement is TPC, the potential across the electrochemical workstation

[0052] (11) is measured through the switches 503 and 504. This potential is converted into current using Ohm’s law, V=IR. The switches 505 and 506 are used for toggling the connection between the DAQ (32) and the sourcemeter (31). At any given point of time, either of these instruments continues to operate. The larger transient (in seconds) is measured using said sourcemeter (31). The shorter transient (milliseconds or microseconds or nanoseconds) is measured using said oscilloscope (30) and DAQ (32), depending on the required resolution. Said oscilloscope (30) or DAQ (32) start measuring the smaller transient once a trigger is received from the function generator (23). The selection of oscilloscope (30) or DAQ (32) for the measurement of shorter transients is done through the customized program created using Lab View software.

[0053] The electronic instruments such as the programmable DC power supplies (22, 16), function generator (23), temperature controller (12), electromagnet controller (13), oscilloscope (30), sourcemeter (31), and DAQ (32) are connected to a computer with Lab View software (40), and can be collectively or individually controlled through customized program created using said Lab View software. The pulsed LEDs and LASERs (21) are also connected to the computer, and are controlled through the customized program created using LabView software.

[0054] Once the type of measurement, i.e., TPV or TPC is selected, the selection of oscilloscope (30) or DAQ (32) for measuring shorter transients is done through the customized program created using LabView software. Any pre-conditioning procedure such as light-soaking, electric polarization, and magnetic polarization are applied to the DUT (10018) through the white LED (20), programmable DC power supply (16), and magnet (130), respectively.

[0055] Once the measurement is initiated, the sourcemeter (31) measures the data from the

[0056] DUT under dark conditions. Through a programmable DC power supply (22), the background illumination from the white LED (20) is shone on the DUT and the sourcemeter (31) starts measuring the larger transient. After a few seconds, the one of the channels of the function generator (23) triggers the oscilloscope (30) or DAQ (32) to start measuring the shorter transient by the pulsed LED or LASER (21), and within milliseconds, the other channel of the function generator (23) triggers the pulsed LED or LASER (21). Within a timespan of milliseconds to nanoseconds, the pulsed LED or LASER (21) is turned off. The background illumination is turned off after a few seconds, and the sourcemeter (31) stops reading the data from the DUT.

[0057] The swapping between the measurement of TPV and TPC, sourcemeter (31) and DAQ (32), and the programmable DC power supply (22) and data acquisition unit (3) is controlled through electronic switches (50). Intensity-dependent measurements are made by varying the intensity of the background illumination with said programmable power supply (22), through regulation of the applied potential and current. The start time and stop time of the background illumination are also controlled through the same power supply (22) via the customized program created using Lab View software. The optical perturbation wavelengths of the pulsed LED or LASER (21), are selected on the basis of the depth of penetration, and the region of interest in the device, namely, bulk or interface. The pulse duration (milli second / nano second) of the smaller perturbation LEDs or LASERs is set through a programmable function generator (23), and the intensity is adjusted by varying the power of the pulsed LED or LASER (21) through customized program created using Lab View software. The intensity of the pulsed LED or LASER (21) is set in such a manner that the photovoltage generated is less than 5% of the photovoltage generated by the bias light. The fitting of the decay of transient photovoltage is either a monoexponential function (AV = A.exp(-t / Trec)) or a biexponential function (AV = AL exp(-t / Treci) + A2.exp(-t / Trec2)) or other reported decay functions, wherein AV is the amplitude of the shorter transient signal, Ai and A2 are proportionality constants, t is the time, and Treci and Trec2 are the two recombination lifetimes of the charge carriers. This provides the recombination lifetime (Tree) of the charge carriers. The lower the value of Tree, the faster the recombination of the charge carriers in the DUT. Transient photocurrent measurements provide information regarding the total charge (AQ) extracted in the device at a particular condition. The total charge extracted can be obtained by integrating the photocurrent decay (J):

[0058] Qext= - f j. dt wherein Qext is the total charge extracted from the device, and J is the measured photocurrent. The rise and fall of photocurrent as a function of time obtained during laser pulse application provides information on charge transport dynamics including transport rate, charge extraction, and trap state distribution.

[0059] In the case of a three-electrode system such as photoelectrochemical devices, specialized sample holders with the provision of conducting measurements with different aqueous or non-aqueous electrolytes are provided. The two illumination sources (20, 21) are focused through the lens assembly onto the same spot on the sample. The signals across the counter electrode (10037) and working electrode (10036) are acquired by the oscilloscope (30), and the electric potential across the reference electrode (10035) and the working electrode (10036) of the device are applied through an electrochemical workstation (11). Thus, the charge transport and recombination properties at each of the applied potential is analyzed by sweeping the potential between certain voltage ranges and measuring the transient behavior at intermittent potential values. Said measurements are conducted with or without the background illumination. A silicon photodetector as in the case of a two- electrode configuration, and Fe20a thin films as in the case of a three-electrode configuration are utilized as the standard materials for the electric and magnetic field-dependent and temperature-dependent transient photovoltage and photocurrent measurements.

[0060] Experimental results

[0061] The data acquired by the sourcemeter (31) is depicted in Figure 6, wherein both smaller transient and larger transient photovoltage signals are displayed. Transient photovoltage (TPV) measurements were conducted at different illumination intensities. As shown in Figure 7, increasing the illumination intensity leads to a higher amplitude of the photovoltage spike. Analyzing the photovoltage decay generates information about the carrier lifetime (T) and recombination dynamics.

[0062] Transient photocurrent (TPC) measurements were conducted at different illumination intensities. As shown in Figure 8, when there is an increase in the intensity, both the photocurrent and the amplitude of the smaller spike increase. By integrating the photocurrent decay, the total extracted charge is determined.

[0063] Before conducting polarization-dependent transient photovoltage measurements, both electric and magnetic field polarization were applied to the device. The electric and magnetic polarization dependent photovoltage data are depicted in Figure 9 and Figure 10 respectively. As the test device is a silicon photodiode, it did not respond to the applied electric and magnetic polarization as silicon is not a non- centrosymmetric material, as can be seen in Figure 9 and Figure 10.

[0064] Said system of the present invention enables the measurement of electric and magnetic polarization-dependent TPV and TPC in a single set-up. Said system enables analysis of extraction and recombination dynamics of the device at interfacial and bulk regions at different measurement conditions for optoelectronic as well as photoelectrochemical devices. Said system enables the use of different pre-conditioning procedures such as light-soaking, temperature, electric polarization, and magnetic polarization. Parameters such as wavelength, illumination intensity, and pulse-width can be varied, as per the requirement. Said system has specialized sample holders for room temperature and variable temperature measurements. Said system is automated by the customized program created using Lab View software. The time-resolved system of the present invention helps study the transient photovoltage and photocurrent decay measurements in any optoelectronic and photoelectrochemical device. Examples of optoelectronic and photoelectrochemical devices include but are not limited to devices for water splitting, carbon dioxide reduction, nitrogen reduction, light emitting diodes, photodetectors, and solar cells. The photovoltage and photocurrent decays provide information about charge transfer dynamics including carrier recombination, transport, carrier extraction, and distribution of trap states.

[0065] In accordance with the various embodiments of the present invention, the objects of the present invention are achieved through a fully automated system for the measurement of TPV and TPC of optoelectronic and photoelectrochemical devices. Said system comprises a plurality of electrode configurations, for conducting experiments in electric fields, magnetic fields, or a combination thereof, whereby measurements can be performed across various temperature ranges, spanning from liquid nitrogen temperature to room temperature and above. Figure 11 shows the temperature-dependent transient photovoltage data wherein with decrease in temperature, an increase in amplitude is obtained.

[0066] According to various embodiments, the system of the present invention for performing a variety of TPV and TPC measurements comprises of sample holder and controllers section (1), light sources and controllers section (2), data acquisition unit (3), electronic switches (50), and a computer with Lab View software (40). Said sample holder and controllers section (1) comprises a sample holder (10), an electrochemical workstation (11), a temperature controller (12), an electromagnet controller (13), pumps (14), a liquid nitrogen tank (15), and programmable DC power supply (16). Said light sources and controllers section (2) comprises light sources (20, 21), function generator (23), power supply for fan (24) used for cooling, and programmable DC power supply (16). Said data acquisition unit (3) comprises an oscilloscope (30), sourcemeter (31), and data acquisition system (DAQ) (32). Said system is interconnected using said electronic switches (50). The components of said system of the present invention are controlled by a computer with a customized program created using Lab View software (40). The sample holders are specific for the measurement of TPV and TPC at room temperature, variable temperature, and photoelectrochemical samples. The device under test (DUT) is placed in the sample holder. The sample designated for the measurement of TPV and TPC is placed in the sample holder, and subjected to the light sources (20, 21) with the focus being on the central part of the DUT. The temperature of the device is varied using a temperature controller (12). A single-pole electromagnet (130) controlled by an electromagnet controller (13) and is used for measurements with magnetic polarization. The photoelectrochemical reactions are measured with an electrochemical workstation (11) with the terminals being connected with the data acquisition unit (3) through electronic switches (50). The electronic switches (50) are connected between the sample holder (10, 1001, 1002, 1003) and said data acquisition unit (3), programmable DC power supply (16, 22), function generator (23), temperature controller (12), electromagnet controller (13), oscilloscope (30), sourcemeter (31) and DAQ (32) which are connected to said computer (40). These are collectively or individually controlled through the customized program created using Lab View software present in the computer.

[0067] It is to be understood, however, that the present invention would not be limited by any means to the components, arrangements, and materials that are not specifically described, and any change to the materials, variations, and modifications can be made without departing from the spirit and scope described in the present invention. 1

Claims

1. I / We claim:

1. A system for the measurement of time-resolved photovoltage (TPV) and time- resolved photocurrent (TPC) of optoelectronic and photoelectrochemical devices characterized by(a) a sample holder and controllers section (1) comprising a sample holder (10), an electrochemical workstation (11), a temperature controller (12), an electromagnet controller (13), pumps (14), a liquid nitrogen tank (15), and programmable DC power supply (16);(b) a light sources and controllers section (2) comprising white LED (20), pulsed LED, or LASER (21), programmable DC supply (22), function generator (23), and power supply for fan (24) of said white LED (20);(c) a data acquisition unit (3) comprising an oscilloscope (30), sourcemeter (31), and data acquisition system (DAQ) (32);(d) electronic switches (50); and(e) a processor (40) for automating said system, wherein, said data acquisition unit (3) is interconnected with said electronic switches (50), and said processor (40) is configured to control and monitor said sample holder and controllers section (1), said light sources and controllers section (2), said data acquisition unit (3), and said electronic switches (50), wherein, data acquisition comprises: i. selection of appropriate sample holder (1001, 1002, 1003);ii. selection of the measurement as TPV or TPC; iii. selection of the data acquisition system as oscilloscope (30) or DAQ (32) for shorter transient; iv. performing pre-conditioning procedures; v. measuring the data from the DUT under dark condition by sourcemeter (31) upon initiation of the program; vi. focusing the background illumination on the DUT from the white LED (20) through a programmable DC power supply (22); vii. initiation of measurement of the larger transient by the sourcemeter (31); viii. triggering the oscilloscope (30) or DAQ (32) by the function generator (23) to initiate the measurement of the shorter transient generated by the pulsed LED or LASER (21); and ix. turning off the background illumination to terminate measurements.

2. The system as claimed in claim 1, wherein the charge generation and extraction dynamics, recombination properties, and distribution of trap states of optoelectronic and photoelectrochemical devices are tested with preconditioning parameters selected from electric field, electrochemical potentials, magnetic field intensities, light-soaking, and temperature regimes.

3. The system as claimed in claim 1, wherein said sample holder (10) is a room temperature sample holder (1001), variable temperature sample holder (1002), or a photoelectrochemical sample holder (1003) for the measurement of TPV and TPC.

4. The system as claimed in claim 1, wherein said sample holder (10) and light sources (20, 21) are placed in a Faraday cage (4) to provide electromagnetic shielding.

5. The system as claimed in claim 1, wherein a device under test (DUT) is placed in said sample holder (10), and subjected to light from said white LED (20), pulsed LED or LASER (21), and the temperature is varied using a temperature controller (12).

6. The system as claimed in claim 1, wherein a single-pole electromagnet (130) controlled by an electromagnet controller (13) is used for performing TPV and TPC measurements with magnetic polarization.

7. The system as claimed in claim 6, wherein said single-pole electromagnet (130) is placed in close proximity to said sample holder (10), and is connected to the terminals (131 and 132) of said electromagnet controller (13).

8. The system as claimed in claim 1, wherein said white LED (20) provides background illumination, and said pulsed LED or LASER (21) provides optical perturbations.

9. The system as claimed in claim 3, wherein said room temperature sample holder(1001) comprises four micromanipulators (10012, 10013, 10014, and 10015) attached to a non -magnetic metallic plate (10011) with a circular section at the center of the plate, wherein the DUT is placed.

10. The system as claimed in claim 9, wherein said micromanipulators (10013 and 10015) measure the signal across said DUT, and said micromanipulators (10012 and 10014) electrically polarize said DUT.

11. The system as claimed in claim 9, wherein said micromanipulators are connected to positive electrode (10022) and negative electrode (10023) of the DUT, and said positive electrode (10022) and negative electrode (10023) are also connected to said data acquisition unit (3) at the other end.

12. The system as claimed in claim 9, wherein said DUT is in the form of a thin film or a single crystal.

13. The system as claimed in claim 9, wherein said system is calibrated and tested by an ultrafast silicon photodiode (10018).

14. The system as claimed in claim 3, wherein variable temperature TPV and TPC measurements are carried out by placing said DUT in a liquid nitrogen-cooled cryostat (10020).

15. The system as claimed in claim 14, wherein a programmable DC power supply (16) is connected to the electrodes of said DUT, and positive electrode (10022) and negative electrode (10023) of said DUT are connected to said data acquisition unit (3).

16. The system as claimed in claim 3, wherein said photoelectrochemical sample holder (1003) comprises of a cell (10034), a reference electrode (RE) (10035), a working electrode (WE) (10036), a counter electrode (CE) (10037), and a single-pole electromagnet (130).

17. The system as claimed in claim 16, wherein said DUT is placed in said cell (10034), and said electrodes are dipped in an electrolyte.

18. The system as claimed in claim 17, wherein said DUT acts as the working electrode (WE), an electrode selected from Ag / AgCl, Standard hydrogen electrode (SHE) and Calomel electrodes is used as the reference electrode (10035), and an electrode selected from platinum, carbon, gold, and nickel is used as the counter electrode (10037).

19. The system as claimed in claim 15, wherein the transient photovoltage is measured between said reference electrode (10035) and said working electrode (10036).

20. The system as claimed in claim 1, wherein said processor (40) controls and monitors said power supply used for the regulation of white bias illumination, sourcemeter (31), function generator (23), oscilloscope (30), data acquisition system (DAQ) (32), and programmable DC power supply (16, 22).

21. The system as claimed in claim 1, wherein said pulsed LED or LASER (21) operates in burst mode based on the parameters selected from duty cycle, number of cycles, period, and frequency.

22. The system as claimed in claim 1, wherein the optical perturbation wavelengths of said pulsed LED or LASER (21) are selected based on the depth of penetration and region of interest.

23. The system as claimed in claim 1, wherein intensity -dependent measurements are performed by varying the intensity of the background illumination with a programmable power supply.

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