Abstract
Mixed lead and tin (Pb-Sn) halide perovskites promise high-performance solar cells because of their narrow bandgaps and other outstanding essential properties. However, there is still a big gap between the performance of the practical devices and theoretical limitations. Here we investigate key factors for realizing high-performance narrow-bandgap Pb-Sn perovskite solar cells (PSCs) via numerical simulations. We first study the effects of extrinsic factors on device performance, which predicts that a p-i-n structure along with appropriate charge transport layers is superior to an n-i-p structure, benefiting from a better energy band alignment. We further investigate key intrinsic factors and demonstrate that surface defect density, body defect density, and film thickness of perovskite absorbers play a pivotal role in determining device performance. The simulation results imply that narrow-bandgap Pb-Sn PSCs with fully-powered optimization should be able to realize a power conversion efficiency of 28.56%. Motivated by the simulations, we also successfully fabricate efficient narrow-bandgap Pb-Sn single-junction and 4-terminal all-perovskite tandem PSCs, which deliver high efficiencies of 21.01% and 26.01% measured under reverse voltage scans, respectively. This work points the way toward the improvement of narrow-bandgap Pb-Sn PSCs in the future.
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•Both extrinsic and intrinsic factors of efficient narrow-bandgap Pb-Sn perovskite solar cells have been investigated.•Pb-Sn perovskite solar cells with an inverted structure are superior to those with a regular structure.•The simulated Pb-Sn perovskite solar cells predict the maximum PCE of 28.56%.•Our fabricated single-junction Pb-Sn perovskite solar cell realized a high PCE of 21.01%.•Our fabricated all-perovskite 4T tandem solar cells realized a high PCE of 26.01%.