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Efficiency boost of bifacial Cu(In,Ga)Se2 thin-film solar cells for flexible and tandem applications with silver-assisted low-temperature process

Abstract

Bifacial Cu(In,Ga)Se2 (CIGS) solar cells are attractive for a range of applications, but their low power conversion efficiency is a limitation. To improve their efficiency, the formation of GaOx at the CIGS/transparent-conducting-oxide interface and charge recombination near this interface under rear illumination need to be suppressed. In the study reported here we prevented the formation of GaOx by silver-promoted low-temperature growth of the CIGS layer. This process also led to an improvement in the absorber quality, a steep Ga gradient near the back interface and reduced the absorption of the transparent conducting oxide. We also report here a certified bifacial solar cell on a glass substrate with efficiencies of 19.77% and 10.89% under front and rear illumination, respectively. We also fabricated bifacial solar cells directly on flexible substrates. Finally, we prepared bifacial perovskite/CIGS tandem solar cells in a four-terminal configuration, achieving a power generation density of 28.0 mW cm-2 under 1 Sun and 30% albedo illumination.

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Fig. 1: Experimental design and material analysis at the CIGS/ITO interface.
Fig. 2: Misfit dislocations in CIGS near the CIGS/ITO interface.
Fig. 3: Photovoltaic (PV) performance under front illumination.
Fig. 4: Photovoltaic performance under rear illumination.
Fig. 5: JSC loss analysis.
Fig. 6: Champion cells and comparison with state-of-the-art bifacial solar cells.
Fig. 7: Bifacial perovskite/CIGS tandem solar cells in four-terminal configuration.

Data availability

All the data generated or analysed during this study are included in the published article and its Supplementary Information. Source data are provided with this paper.

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Acknowledgements

This work received funding from the Swiss Federal Office of Energy (SFOE; SI/502310-01 ‘ACIGS’) and was partially supported by the Young Scholar Fellowship Einstein Program of MOST, Taiwan (grant no. MOST 110-2636-E-007-015). H.L. is grateful for the funding of the China Scholarship Council (CSC) of the Ministry of Education of the People’s Republic of China. This project received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 850937. The authors also acknowledge the financial support from the Strategic Focus Area Advanced Manufacturing under the project AMYS - Advancing manufacturability of hybrid organic-inorganic semiconductors for large area optoelectronics. The authors acknowledge use of the UHRTEM (C.-C. Chi) and HRTEM (Y.-J. Yu) equipment belonging to the Instrumentation Center at National Tsing Hua University in Taiwan and FIB (W.-N. Lee) at CNMM of the National Tsing Hua University in Taiwan.

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Contributions

S.-C.Y. proposed the research. R.C. and A.N.T. supervised the work. S.-C.Y. designed the experiments, fabricated all CIGS devices and conducted the characterizations. T.-Y.L. carried out the STEM and TEM measurements. M.O. and R.C. performed the optical and numerical simulations. H.L. fabricated perovskite top cells and assisted with the bifacial and tandem solar cell measurements. R.K. performed the laser scribing on PI samples. F.F. supervised the work on perovskite solar cells and instructed the experimental and characterization designs of the bifacial tandem solar cells. S.-C.Y. wrote the manuscript with inputs from all other co-authors.

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Correspondence to Shih-Chi Yang.

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Yang, SC., Lin, TY., Ochoa, M. et al. Efficiency boost of bifacial Cu(In,Ga)Se2 thin-film solar cells for flexible and tandem applications with silver-assisted low-temperature process. Nat Energy 8, 40–51 (2023). https://doi.org/10.1038/s41560-022-01157-9

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