An antibonding valence band maximum enables defect-tolerant and stable GeSe photovoltaics
Shunchang Liu, Chen‐Min Dai, Yimeng Min, Yi Hou, Andrew H. Proppe, Ying Zhou, Chao Chen, Shiyou Chen, Jiang Tang, Ding‐Jiang Xue, Edward H. Sargent, Jin‐Song Hu
Abstract
Abstract In lead–halide perovskites, antibonding states at the valence band maximum (VBM)—the result of Pb 6 s -I 5 p coupling—enable defect-tolerant properties; however, questions surrounding stability, and a reliance on lead, remain challenges for perovskite solar cells. Here, we report that binary GeSe has a perovskite-like antibonding VBM arising from Ge 4 s -Se 4 p coupling; and that it exhibits similarly shallow bulk defects combined with high stability. We find that the deep defect density in bulk GeSe is ~10 12 cm −3 . We devise therefore a surface passivation strategy, and find that the resulting GeSe solar cells achieve a certified power conversion efficiency of 5.2%, 3.7 times higher than the best previously-reported GeSe photovoltaics. Unencapsulated devices show no efficiency loss after 12 months of storage in ambient conditions; 1100 hours under maximum power point tracking; a total ultraviolet irradiation dosage of 15 kWh m −2 ; and 60 thermal cycles from −40 to 85 °C.