Electrochemically Deposited CZTSSe Thin Films for Monolithic Perovskite Tandem Solar Cells with Efficiencies Over 17

• Published in: Energy & environmental materials (Hoboken, N.J.) Vol. 7; no. 1
• Main Authors: Hwang, Sun Kyung, Park, Ik Jae, Seo, Se Won, Park, Jae Hyun, Park, So Jeong, Kim, Jin Young
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01.01.2024
• Subjects: Cell surface; CZTSSe; monolithic tandem solar cells; perovskite; Perovskites; Photovoltaic cells; Solar cells; solution process; Surface roughness; surface roughness control; Thin films
• ISSN: 2575-0356; 2575-0356
• DOI: 10.1002/eem2.12489

In spite of the high potential economic feasibility of the tandem solar cells consisting of the halide perovskite and the kesterite Cu2ZnSn(S,Se)4 (CZTSSe), they have rarely been demonstrated due to the difficulty in implementing solution‐processed perovskite top cell on the rough surface of the bottom cells. Here, we firstly demonstrate an efficient monolithic two‐terminal perovskite/CZTSSe tandem solar cell by significantly reducing the surface roughness of the electrochemically deposited CZTSSe bottom cell. The surface roughness (Rrms) of the CZTSSe thin film could be reduced from 424 to 86 nm by using the potentiostatic mode rather than using the conventional galvanostatic mode, which can be further reduced to 22 nm after the subsequent ion‐milling process. The perovskite top cell with a bandgap of 1.65 eV could be prepared using a solution process on the flattened CZTSSe bottom cell, resulting in the efficient perovskite/CZTSSe tandem solar cells. After the current matching between two subcells involving the thickness control of the perovskite layer, the best performing tandem device exhibited a high conversion efficiency of 17.5% without the hysteresis effect. Monolithic two‐terminal perovskite/CZTSSe tandem solar cells with a power conversion efficiency of 17.5% are demonstrated by a potentiostatic electrochemical deposition and ion milling of the CZTSSe bottom cell for roughness control, which enables uniform deposition of perovskite top cells via solution process.