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.

混合铅和锡 (Pb-Sn) 卤化物钙钛矿因其窄带隙和其他突出的基本特性而有望成为高性能太阳能电池。然而，实际器件的性能与理论限制之间仍有很大差距。在这里，我们通过数值模拟研究了实现高性能窄带隙 Pb-Sn 钙钛矿太阳能电池 (PSC) 的关键因素。我们首先研究了外部因素对器件性能的影响，这预测了 pin 结构以及适当的电荷传输层优于 nip 结构，这得益于更好的能带排列。我们进一步研究了关键的内在因素，并证明钙钛矿吸收体的表面缺陷密度、体缺陷密度和薄膜厚度在确定器件性能方面起着关键作用。仿真结果表明，全功率优化的窄带隙 Pb-Sn PSC 应该能够实现 28.56% 的功率转换效率。在模拟的推动下，我们还成功地制造了高效的窄带隙 Pb-Sn 单结和 4 端全钙钛矿串联 PSC，在反向电压扫描下测量的效率分别为 21.01% 和 26.01%。这项工作为未来改进窄带隙 Pb-Sn PSC 指明了方向。分别在反向电压扫描下测得 01% 和 26.01%。这项工作为未来改进窄带隙 Pb-Sn PSC 指明了方向。分别在反向电压扫描下测得 01% 和 26.01%。这项工作为未来改进窄带隙 Pb-Sn PSC 指明了方向。