Rational band offset engineering in perovskite solar cells through HTL-side bandgap grading

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Chinese explanation / 中文解读

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Original abstract

The band alignment plays a decisive role in determining the performance of perovskite solar cells (PSCs). In this study, the absorber back-side, a region between triple-cation perovskite layer and CuInS 2 (CIS) hole transporting layer (HTL) is engineered to optimize band alignment and reduce interfacial recombination. A fabricated PSC is reproduced using SCAPS, employing a combination of experimentally-extracted and literature-reported parameters. A 200 nm optimal grading depth reveals a negatively-sloped efficient relationship between the valence and conduction band offsets (VBO and CBO) at the perovskite back-side. The optimized model utilizes a bandgap energy (E g ) of 1.78 eV, and an electron affinity (EA) of 3.03 eV at the CIS/perovskite interface, which leads to about 21.8% improvement of efficiency. This band engineering creates a selective interface through proper VBO for efficient hole extraction, and proper CBO to block electrons. Consequently, it reduces interfacial recombination, enhances internal electric field strength, and significantly increases V OC and FF, with a small effect on J SC . Moderate negative CBOs near CIS are generally beneficial because it suppresses electron back-transfer and reduces recombination. The excessive negative VBOs in the graded structure, increase holes transport resistance, and result in S-shaped J-V distortion. The FF degradation trend appears when extraction barriers form, regardless of CBO.

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