Method for testing UV degradation of a solar cell
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- HANWHA Q CELLS GMBH
- Filing Date
- 2024-07-19
- Publication Date
- 2026-06-10
Smart Images
Figure DE2024100647_06022025_PF_FP_ABST
Abstract
Description
[0001] Method for testing UV degradation of a solar cell
[0002] The invention relates to a method for testing UV degradation of a solar cell. Solar modules or solar cells installed therein exhibit degradation after installation in the field due to various effects. Various methods for testing UV degradation, i.e., UV-induced degradation, are known. For example, UV degradation can be detected using a UV LED or a UV laser, as described, for example, in US 2018 / 0041165 A1. However, these methods are time-consuming, particularly if a UV dose is to be simulated in the field over a longer period of time, i.e., more than two years. However, there is a need for a method for testing the UV degradation of a solar cell that requires a shorter period of time.
[0003] It is an object of the invention to provide a method for testing UV degradation of a solar cell which can be carried out relatively quickly.
[0004] The invention relates to a method for testing UV degradation of a solar cell, comprising the following steps: a) irradiating at least one partial area of a solar cell with a pulsed UV laser, b) performing a photoluminescence measurement on a surface of the irradiated partial area and a further, unirradiated partial area of the solar cell, and c) evaluating the UV degradation of the solar cell by comparing measured values of the at least one irradiated partial area and the unirradiated partial area obtained by means of the photoluminescence measurement carried out.
[0005] Using the method according to the invention, the determination of UV degradation of a solar cell and, by extension, of a solar module containing the solar cell over a service life of > 20 years is significantly accelerated. Using high laser intensity, the UV degradation test can be significantly accelerated, so that UV doses equivalent to 25 years in the field can be applied within a few hours in step a). The at least one partial area in step a) is limited. Step b) can be implemented by recording a photoluminescence image of the entire solar cell. Using automated photoluminescence image analysis, grayscale differences observed in step c) can then be converted into a power loss, thus enabling simple predictions of UV degradation in the field.The at least one partial area treated in step a) is characterized by a lower gray value as the measured value compared to the other, unirradiated partial area not treated in step a). These measured values are compared in step c), allowing the power loss to be calculated and the UV-induced degradation to be derived. The process is also cost-effective. The power consumption is relatively low compared to a UV test chamber with mercury vapor lamps or Xe arc lamps with UV filters.
[0006] For the purposes of this invention, the term "solar cell" refers to a semiconductor structure having a pn junction and, in a final state, intended for use in converting sunlight into electrical energy. The solar cell feature does not require the semiconductor structure to have all the structural features of a fully processed solar cell. For example, anti-reflective layers and / or metallized electrode structures may still be missing. This means that even a partially processed semiconductor structure with a pn junction fulfills the feature of a "solar cell" within the meaning of the present invention.
[0007] In a preferred embodiment, the at least one partial area is scanned with a meandering line pattern in step a). By repeatedly scanning the at least one partial area in a meandering pattern, a desired irradiance in kWh / m2 Preferably, the irradiation of the at least one partial area in step a) is carried out in several passes until a predetermined time period or preferably a predetermined UV dose is reached in the at least one partial area. The time of one pass is preferably <2 seconds, more preferably <1 second.
[0008] In a preferred embodiment, in step a), adjacent laser pulses are applied to the surface of the solar cell at a distance of 8 to 12 pm from one another. Preferably, the at least one partial region is scanned in a meandering pattern, for example, by applying adjacent laser pulses offset by 8 to 12 pm from one another to the surface of the at least one partial region using a deflection optic such as a deflection mirror.
[0009] Preferably, adjacent laser pulses overlap in step a). The diameters of the laser pulses on the surface of the at least one partial region are, for example, in the range of 900 to 500 pm, e.g., 700 pm, so that adjacent laser pulses overlap.
[0010] Preferably, step a) is performed using a slit mask with at least one slit, which at least partially covers the solar cell, so that the at least one partial region is slit-shaped. The at least one partial region is delimited and / or defined by the slit mask. The slit mask preferably has at least two slits, more preferably at least three slits. This simplifies the evaluation in step c). The slits have, for example, a size of 18 x 1 mm.
[0011] While the at least one partial region irradiated in step a) is defined by the at least one slit, the further, unirradiated partial region used for analysis or evaluation in step c) is preferably located under the slit mask in step a). Preferably, the further, unirradiated partial region used in step c) is adjacent or substantially adjacent to the partial region irradiated in step a). This minimizes inhomogeneities in the evaluation due to the wafer material or the dielectric layers of the solar cell.
[0012] In a preferred embodiment, the area scanned in step a) is larger than the slit in the slit mask. This minimizes edge effects caused by the generated Gaussian laser beam profile. If the slit has a size of 18 x 1 mm, for example, the area scanned in step a) is 18.5 x 1.5 mm.
[0013] The solar cell is preferably a partially processed cell with dielectric passivation layers on its front and rear sides and is metallization-free or unmetallized. Therefore, the partially processed solar cell preferably has dielectric passivation layers such as SiOx, SiNx, poly-Si, or AlOx on both its front side (i.e., the side facing away from the light incidence) and its rear side (i.e., the side facing away from the light incidence) and is unmetallized on both its front and rear sides (i.e., it has neither front nor rear electrodes).
[0014] The solar cell used in the process can be any type of solar cell, e.g., a PERC (Passivated Emitter and Rear Cell), HIT (Heterojunction with Intrinsic Thin Layer), or IBC (Interdigitated Back Contact) solar cell. The solar cell is preferably a partially processed TOPCon (Tunnel Oxide Passivated Contact) solar cell. High-efficiency solar cells are generally more sensitive to UV degradation. Therefore, high-efficiency solar cells such as TOPCon solar cells are particularly suitable for use in the process according to the invention.
[0015] In a preferred embodiment, a pulse power of the UV laser used in step a) is set such that the solar cell is not heated above 50°C. Alternatively or additionally, a frequency or pulse repetition frequency of the UV laser used in step a) is preferably set such that the solar cell is not heated above 50°C. By these measures, degradation effects, e.g. in the bulk, such as LeTID (Light and Elevated Temperature Induced Degradation), are prevented or at least reduced. By using a pulsed UV laser with a suitable pulse length, energy and repetition frequency, heating of the solar cell > 50°C can be prevented. For example, the frequency is set to 100 kHz, while a pulse power, e.g., is set to 17.2 W in order to heat the solar cell to > 50°C. The UV laser is pulsed and preferably has a pulse length < 100 ns, more preferably < 50 ns.The UV laser preferably has a power of approximately 10 - 20 watts.
[0016] The UV laser preferably has a wavelength of <380 nm. For example, the UV laser is a frequency-tripled Nd:YAG laser at 355 nm, a frequency-tripled fiber laser at 343 nm, or an excimer laser such as a XeCl laser with a wavelength of 308 nm. Preferably, in addition to the UV laser, a deflection and / or beam optics are used in step a).
[0017] By scanning at least one partial area multiple times, the desired UV dose or irradiance can be set, while a high pulse repetition frequency, e.g. of 100 kHz and intensity, e.g. > 10 kW / mm 2 The UV laser allows high UV doses of, for example, > 1000 kWh / m2 to be achieved in a relatively short treatment time. This further results in time and cost savings and lower power consumption.
[0018] Preferably, the UV laser is adjusted in such a way that in step a) it produces UV doses > 1000 kWh / m 2achieved. For example, in one pass of step a), 36,000 laser pulses are applied per sub-area, preferably per slit of the slit mask. At a pulse frequency of 100 kHz, the scanning of this sub-area or slit takes only approximately 0.36 seconds, whereby due to mechanical limitations such as the movement of a deflection and / or beam optics, a scanning of a sub-area or slit takes approximately 0.8 seconds. With three sub-areas or slits, the duration of step a) is a total of approximately 2.3 - 2.5 seconds. In step b), the at least one sub-area and the at least one further, unirradiated sub-area are examined, preferably using calibrated photoluminescence. In step c), a profile of the gray values thus obtained can be corrected and / or standardized. By comparison with a calibrated reference, i.e.of a solar cell with known degradation over the entire area, which represents the gray value, the degradation in the area of at least one partial area can be determined.
[0019] Further features and advantages of the invention are described in connection with preferred embodiments, which are explained in more detail with the aid of the following figures.
[0020] They show:
[0021] Fig. 1 is a sketched representation of a step of a method according to the invention; and
[0022] Fig. 2 is a plan view of the solar cell with slit mask shown in Fig. 1.
[0023] Fig. 1 shows a sketched representation of a step of a method according to the invention. Fig. 1 shows step a) of the method according to the invention, in which a partial region 7 of a solar cell 4 is irradiated with a pulsed UV laser 1. The device used in this step comprises the UV laser 1, a deflecting mirror 2, and a beam optics 5. A slit mask 3 is arranged on the solar cell 4 and has three slits 6, purely by way of example. In step a), the UV laser 1 emits a laser beam, as illustrated by an arrow, which is directed by the deflecting mirror 2 and the beam optics 5 onto one of the three partial regions 7. The deflecting mirror 2 is adjustable, as shown by a dashed arrow. The irradiation of one of the three partial regions 7 in step a) is carried out in a meandering manner in several passes until a predetermined time period or a predetermined UV dose is reached in the partial region 7.The time of one pass is < 2 seconds. In step a), adjacent laser pulses are offset by 8 to 12 pm from each other using the deflection mirror 2 and overlap. The meandering irradiation using the UV laser 1 is also performed for the other two of the three sub-areas 7.
[0024] Following step a), in a step b) not shown in Fig. 1, a photoluminescence measurement is carried out on a surface of the irradiated partial area and a further, unirradiated partial area 8 of the solar cell 4, e.g. by taking a photoluminescence image of the area of the partial areas 7 and the partial area 8 or of the entire surface of the solar cell 4. The unirradiated partial area 8, which is used for the analysis or evaluation described below, is located under the slit mask 3 while step a) is being carried out. The unirradiated partial area 8 is adjacent or substantially adjacent to the irradiated partial area 7. Following step b), in a step c) not shown in Fig. 1, the UV degradation of the solar cell 4 is assessed by comparing measured values of the partial areas 7 and the further, unirradiated partial area 8 obtained by means of the photoluminescence measurement carried out.
[0025] Fig. 2 shows a top view of the solar cell with slit mask shown in Fig. 1. The slit mask 3 is arranged on the solar cell 4. It has three slits 6, each measuring, for example, 18 x 1 cm. The surface of the solar cell 4 exposed in the slits 6 represents the partial regions 7, while the surface beneath the slit mask 3 represents the further, unirradiated partial region 8, which is not actually visible in Fig. 2 but is marked for clarity. In step a) shown in Fig. 1, approximately 36,000 laser pulses are applied per pass, with a desired irradiance being set by repeatedly scanning each slit 6 in a meandering pattern. List of reference symbols:
[0026] 1 UV laser
[0027] 2 deflecting mirrors
[0028] 3 slit mask
[0029] 4 solar cells
[0030] 5 Beam optics
[0031] 6 slots
[0032] 7 sub-area
[0033] 8 further, unirradiated areas
Claims
Patent claims: 1 . Method for testing UV degradation of a solar cell (4), comprising the following steps: a) irradiating at least one partial area (7) of a solar cell (4) with a pulsed UV laser (1), b) carrying out a photoluminescence measurement on a surface of the at least one irradiated partial area (7) and a further, unirradiated partial area (8) of the solar cell (4), and c) evaluating the UV degradation of the solar cell by comparing measured values of the at least one irradiated partial area (7) and the unirradiated partial area (8) obtained by means of the photoluminescence measurement carried out.
2. Method according to claim 1, characterized in that the at least one partial area (7) is scanned with a meandering line pattern in step a).
3. Method according to claim 1 or 2, characterized in that the irradiation of the at least one partial area (7) in step a) is carried out in several passes until a predetermined time period or a predetermined UV dose is reached in the at least one partial area (7), wherein a time of one pass is preferably < 2 seconds, preferably < 1 second.
4. Method according to one of the preceding claims, characterized in that in step a) adjacent laser pulses are applied to the surface of the solar cell (4) offset by 8 to 12 pm from one another and / or in step a) adjacent laser pulses overlap.
5. Method according to one of the preceding claims, characterized in that the UV laser in step a) has a pulse length < 100 ns.
6. Method according to one of the preceding claims, characterized in that step a) is carried out using a slit mask (3) with at least one slit (6) which at least partially covers the solar cell (4) so that the at least one partial region (7) is slit-shaped, wherein the slit mask (3) preferably has at least two, more preferably three slits (6).
7. Method according to claim 6, characterized in that the area scanned in step a) is larger than the slit (6) in the slit mask (3).
8. Method according to one of the preceding claims, characterized in that the solar cell (4) is a partially processed solar cell with dielectric passivation layers on its front and back sides and is free of metallization, preferably a partially processed TOPCon solar cell.
9. Method according to one of the preceding claims, characterized in that a pulse power and / or frequency of the UV laser (1) used in step a) is or are set such that the solar cell (4) is not heated above 50° C.
10. Method according to one of the preceding claims, characterized in that the UV laser (1) is adjusted such that in step a) it produces UV doses > 1000 kWh / m 2 reached.