An all-perovskite tandem cell based on narrow-bandgap mixed tin–lead (Sn–Pb) alloyed perovskites is a potential photovoltaic device whose power conversion efficiency can exceed the Shockley–Queisser limit of a single-junction solar cell, 33%. However, comprehensive descriptions of the charge-carrier mobilities and transport mechanisms in the mixed Sn–Pb perovskite system remain elusive. Herein, we integrate density functional theory (DFT) calculations with charge transport models to provide more insight into the electronic structures and transport behaviors of these materials. We specifically employ a model using large polaron transport based on LO phonon scattering and ionized impurity scattering due to the oxidation of Sn²⁺ to Sn⁴⁺. DFT simulations revealed that there is a crossover in the electronic properties of pure-Sn and pure-Pb perovskites at Pb contents of more than 0.5, which causes increasing reduced effective mass as the Pb content increases. Theoretical calculations for charge-carrier mobility were in agreement with the experimental data between 23 and 89 cm² V⁻¹ s⁻¹ at room temperature. In mixed Sn–Pb perovskites, LO phonon scattering predominates. However, in pure-Sn perovskites, transport scatterings based on LO phonon and ionized impurity scatterings are important. This discovery advances our knowledge of the transport mechanisms underlying the system of mixed Sn–Pb compounds.

中文翻译：

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杂化有机-无机混合 Sn-Pb 合金钙钛矿中的电子结构和电荷传输迁移率


基于窄带隙混合锡-铅 （Sn-Pb） 合金钙钛矿的全钙钛矿叠层电池是一种潜在的光伏器件，其功率转换效率可以超过单结太阳能电池的 Shockley-Queisser 极限 33%。然而，对混合 Sn-Pb 钙钛矿系统中的电荷载流子迁移率和传输机制的全面描述仍然难以捉摸。在此，我们将密度泛函理论 （DFT） 计算与电荷传输模型相结合，以更深入地了解这些材料的电子结构和传输行为。我们特别采用了一种基于低极化子散射和由于 Sn²⁺ 氧化成 Sn⁴⁺ 而导致的电离杂质散射的模型。DFT 模拟表明，当 Pb 含量超过 0.5 时，纯 Sn 和纯 Pb 钙钛矿的电子性质存在交叉，这会导致随着 Pb 含量的增加而降低的有效质量增加。电荷载流子迁移率的理论计算与室温下 23 至 89 cm^{2 V-1 s-1} 之间的实验数据一致。在混合 Sn-Pb 钙钛矿中，LO 声子散射占主导地位。然而，在纯 Sn 钙钛矿中，基于 LO 声子和电离杂质散射的输运散射很重要。这一发现加深了我们对混合 Sn-Pb 化合物系统潜在转运机制的认识。