Influence of Ga back grading on voltage loss in low‐temperature co‐evaporated Cu(In, Ga)Se2 thin film solar cells. (15th March 2021)

• Record Type: Journal Article
• Authors: Yang, Shih‐Chi; Ochoa, Mario; Hertwig, Ramis; Aribia, Abdessalem; Tiwari, Ayodhya N.; Carron, Romain
• Is Part Of: Progress in photovoltaics. Volume 29:Number 6(2021)
• Page Start: 630
• Page End: 637
• Publication Date: 2021-03-15
• Subjects: back interface recombination -- Ga back grading -- TRPL lifetime -- VOC deficit; Solar cells -- Periodicals; Photovoltaic cells -- Periodicals; Solar power plants -- Periodicals; 621.31245
• DOI: 10.1002/pip.3413
• Languages: English
• ISSNs: 1062-7995

Abstract

Abstract: The performance of Cu(In, Ga)Se2 (CIGS) solar cells is limited by the presence of the highly recombinative CIGS/Mo interface. The recombination at the CIGS/Mo interface is influential for the open circuit voltage ( V OC ) in high quality CIGS absorbers with increased charge carriers diffusion length. A quantitative understanding of the role of the Ga back grading height (ΔGGI) in suppressing back interface recombination is needed. In this work, we take advantage of a low temperature process to modify the ΔGGI while keeping the composition in the notch and front regions almost unchanged. Improvement in both V OC deficit and time‐resolved photoluminescence lifetime are observed with increasing ΔGGI. With a combination of back surface modification experiments and numerical simulations, we quantify a voltage loss in ungraded devices of approximately 100 mV solely from the back interface recombination. Nice agreement between simulation and experimental data is reached while constraining the values of possible diffusion lengths. Our results suggest that a ΔGGI of about 0.50 is required to effectively suppress the back interface recombination, highlighting the importance of grading control in high‐performance CIGS solar cells and devices. Abstract : This study investigates the influence of Ga back grading on the electrical loss in CIGS solar cells by taking advantage of low‐temperature and early stage In‐free process. Both V OC deficit and TRPL decays suggest a non‐negligible voltage loss for ΔGGI at least up to 0.5 (ΔEg ~320 meV). By combining with numerical simulation, we quantify a voltage loss in ungraded devices of approximately 100 mV solely from the back interface recombination.