Atsushi Masuda

This study investigated mitigation methods for shunting-type potential-induced degradation (PID-s) in wafer-based standard p-type crystalline silicon technology. Li did not cause PID-s, whereas Na caused substantial PID-s. To quantitatively explore their relationship, we used a module without a cover glass and an additional encapsulation material on the solar cell’s light-receiving surface. We then performed PID tests with Li and Na contamination. Moreover, we measured the current density–voltage characteristics and captured electroluminescence images during the test. We performed secondary ion mass spectrometry on certain modules. When Na was present, the performance degradation of the solar cell remained the same as that of typical PID-s, although introducing Li substantially decelerated the performance degradation. Concurrently, the long-term PID test showed that performance degradation occurred even at a low Na concentration (−1 ). This indicates that Li can only mitigate, but not inhibit, PID-s when Na is present.

In this study, the structural, compositional, and electrical properties of nanocrystalline silicon/silicon oxide (nc-Si/SiO _x ) composite films fabricated by plasma-enhanced chemical vapor deposition were investigated for high-performance Si solar cells. The Si-rich layers in the composite layer precursor were deposited using various [CO ₂ ]/([SiH ₄ ] + [CO ₂ ]) flow rate ratios and post-deposition annealing was performed to induce nc-Si formation. Auger electron spectroscopy confirmed that the Si/O ratio of the Si-rich layers can be tuned by the gas flow rate ratio. Cross-sectional transmission electron microscope images revealed nc-Si formation was promoted and its areal density increased by decreasing the gas flow rate ratio. The passivation performance exhibited a clear optimum at an oxygen concentration of ∼5 at.%, whereas both higher and lower O contents degraded the effective carrier lifetime. In contrast, the electrical resistance increased monotonically with O concentration, suggesting improved carrier transport in Si-rich films with higher nc-Si density. No trade-off was observed between conductivity and passivation, demonstrating that both can be independently optimized. These results show that controlling the gas flow rate ratio and annealing enables simultaneous improvement of passivation and carrier conduction in nc-Si/SiO _x layers.

Tandem solar cells composed of perovskite top cell and silicon bottom cell are challenging key technologies for breaking the theoretical efficiency limit of crystalline silicon solar cells. After important report by Helmholtz-Zentrum Berlin group in 2020 [1] using self-assembled monolayer hole transport material in the top cell and rear-emitter structure in silicon heterojunction bottom cell, many reports on high efficiency over 30% have been presented. Recently, LONGi reported that the highest efficiency of 34.6% in 2024 [2]. However, there are two issues to be solved for commercialization of perovskite/silicon tandem solar cells. One is reliability issue such as stability against heat, moisture, and light irradiation, etc. Current decrease in the top cell by degradation disturbs the current matching in the two-terminal structure. Not only indoor acceleration tests but also outdoor exposure tests are important for judging reliability. The other is how to fabricate perovskite/silicon tandem photovoltaic modules. Since perovskite/silicon tandem photovoltaic modules are key technologies for increasing efficiency of crystalline silicon photovoltaic modules, similar module-fabrication technologies to conventional crystalline silicon photovoltaic modules are required using vacuum laminator and encapsulant materials. However, conventional ethylene-vinyl acetate copolymer encapsulant needs high temperatures around 150 degree Celsius for lamination. The lamination temperatures around 150 degree Celsius are far higher than the temperatures keeping perovskite solar cells stable without degradation. In this talk many reliability test results obtained indoors and outdoors will be introduced. Origins for chemical or mechanical degradation will be discussed based on the reaction occurring in materials used in solar cells or photovoltaic modules induced by stresses such as heat, moisture, and light irradiation. Sophisticated low-temperature module-fabrication processes below 100 degree Celsius using silicone encapsulants developed by the author's group will be also introduced. This work is in part supported by the New Energy and Industrial Technology Development Organization. [1] A. Al-Ashouri et al., Science 370 , 1300 (2020). [2] M. Green et al., Prog. Photovolt. 33 , 3 (2025).

Tandem solar cells composed of perovskite and crystalline Si (c-Si) has attracted much attention as a trump card to break through the theoretical efficiency limit of c-Si solar cells. In order to replace c-Si photovoltaic modules, it is important that the module fabrication process should be as identical as possible to the current one. In the most conventional module fabrication processes for c-Si solar cells, all the module components, including the cells, are heated to approximately 150 °C during lamination. However, the performances of perovskite solar cells are degraded at temperatures above 100 °C. Therefore, the module fabrication process of lamination applicable to perovskite/Si tandem solar cells should be carried out below 100 °C. In this study, silicone sheets were examined for encapsulating perovskite/Si tandem solar cells at lower temperatures than that in the current encapsulation processes. As a result, the highest efficiency of the fabricated module after lamination reached 28.8% (in house).

A new concept of unencapsulated photovoltaic (PV) modules was developed to avoid several degradation phenomena caused by encapsulation materials, to facilitate recycling of PV modules. The reliability and durability of the new concept module were investigated through damp heat (DH) and thermal cycling (TC) tests. The maximum output power of the new concept module did not decrease significantly after 3000 h of DH testing and 1200 cycles of TC testing. Furthermore, no significant decrease was also observed in sequential testing of the total of 1800 h of DH testing and 600 cycles of TC testing. It was also found that UV absorbers prevent degradation of polycarbonate cover material used to enable to be lightweight and installed on curved surface and that MgF₂ coating on cover material suppresses reflection loss of incident light. These experimental results indicate that unencapsulated PV modules are reliable enough for replacing conventional modules.

The purpose of this study was to investigate the long‐term reliability of various photovoltaic technologies in Japan under humid subtropical climatic conditions. The five investigated technologies were p‐type aluminum back surface field (Al‐BSF) single‐crystalline silicon (p‐type Al‐BSF sc‐Si), p‐type Al‐BSF multi‐crystalline silicon (p‐type Al‐BSF mc‐Si), copper indium gallium (di)selenide (CIGS), hydrogenated amorphous silicon (a‐Si:H), and a‐Si:H and hydrogenated microcrystalline silicon tandem (a‐Si:H/μc‐Si:H) photovoltaic modules. The monthly performance ratio (PR) was calculated based on the power outputs of the photovoltaic arrays and global solar irradiance in the same plane as the photovoltaic arrays, which were measured at 10‐min intervals over 12 years. The PR was corrected to 25°C (PR_T=25) as defined by the standard test conditions. Furthermore, the power outputs of all the photovoltaic modules were measured by a pulsed solar simulator (indoor flash testing) from 2012 to 2019. The PR and PR_T=25 values showed that the annual degradation rates of the p‐type Al‐BSF sc‐Si, p‐type Al‐BSF mc‐Si, CIGS, a‐Si:H/μc‐Si:H, and a‐Si:H photovoltaic modules were approximately 0.0%/year, 0.2%/year, 1.1%/year, 0.6%/year, and 1.2%/year, respectively, which were consistent with the results of the indoor flash testing. These results indicate that p‐type Al‐BSF sc‐Si and mc‐Si photovoltaic modules can show little annual degradation and should retain high, stable power generation performance for over 20 years. In contrast, the higher annual degradation rates of the investigated thin‐film photovoltaic technologies suggest that they did not maintain performance of over 90% of the nominal power outputs even for 12 years.

The purpose of this study is to improve both the design of photovoltaic (PV) modules and their efficiency by utilizing long-wavelength light. A black back sheet (BS) with IR reflection was examined for this purpose. In this study, the damp heat (DH) test, thermal cycle (TC) test, and light irradiation test were carried out for crystalline Si PV modules using black BS without light reflection, black BS with IR reflection, and conventional white BS. The external quantum efficiency of perovskite/Si tandem PV modules was measured to confirm the effective utilization of long-wavelength light. Suppression of the decrease in both open-circuit voltage and fill factor was achieved using black BS with IR reflection by mitigating the elevation of cell temperature. These results suggested the long-term reliability of black BS with IR reflection against the DH test, TC test, and light irradiation test, and its effectiveness for perovskite/Si tandem PV modules.

In order to increase the photocurrent of tandem solar cells with a silicon (Si) solar cell as the bottom cell, we investigate the relationship between the localized surface plasmon resonance effect of gold nanoparticles (AuNPs) and the arrangement of AuNPs onto solar cells. AuNPs were deposited on P-type crystalline Si (c-Si) cells and Si heterojunction (SHJ) type cells. To obtain the localized surface plasmon resonance effect, the shape, size, and arrangement of the nanostructures are important. Especially, arrangement of AuNPs onto solar cells was inquired in this study because these parameters must be adjusted appropriately to produce a plasmon resonance in a specific wavelength range. It was found that the plasmon resonance effect is significant when deposited on the surface of c-Si cell rather than on top of the Ag electrode. AuNPs deposition on the c-Si cell surface leads to not only the localized surface plasmon resonance effect but also improvement in charge transport between the c-Si cell surface and Ag electrode. However, in the SHJ-type cells, the plasmon resonance effect was not observed because the surface layer was composed of a W-doped In₂O₃ (IWO) layer.

This paper particularly explains potential-induced degradation (PID) of wafer-based standard p-type crystalline silicon technology. We present a single-encapsulation method that is useful for simulating PID in the laboratory to facilitate microanalyses of module-level solar cells. The PID testing is performed for the module with single-encapsulation and conventional modules. Their current–voltage characteristics and electroluminescence images are investigated before and after the PID tests. As described herein, we infer that the single-encapsulation modules generate PID almost in the same way as conventional modules do, and that the degradation trend is almost identical to that of conventional modules. Results of PID recovery tests indicate that the time necessary for PID recovery is always less than that for PID generation, irrespective of the encapsulation method.

現在主流であるp型単結晶裏面不動態（PERC）太陽電池に置き換わる技術として，n型単結晶Siウエハを用いた各種太陽電池の研究開発が進展している。一方で，結晶Si太陽電池の変換効率は商用サイズウエハにおいても理論限界効率に迫りつつある。さらなる変換効率向上には異なるバンドギャップの太陽電池を組み合わせた多接合化の技術開発が必要である。最近では，ペロブスカイト太陽電池と組み合わせたペロブスカイト／結晶Siタンデム太陽電池が注目されている。変換効率の向上に加え，信頼性の向上による生涯発電量最大化が太陽光発電のいっそうの普及拡大に必要不可欠である。太陽電池モジュールの発電性能の低下要因と信頼性向上のために必要なモジュール技術についても言及する。