Tin–Lead Alloying for Efficient and Stable All-Inorganic Perovskite Solar Cells

Cesium-containing all-inorganic perovskites have received considerable interest in photovoltaics research because of their potential for improved stability compared to their organic–inorganic hybrid counterparts. However, the inorganic perovskites studied thus far still suffer from lower power conversion efficiency and long-term instability due to an unfavorable bandgap and either phase instability or air sensitivity. Herein, a strategy to mitigate these concerns is investigated by alloying tin and lead on the B site to form tin–lead-alloyed low-bandgap (∼1.34 eV) inorganic CsSn0.3Pb0.7I3 perovskites. Solar cells made using this material in a full device architecture with PEDOT/PSS hole transport materials (HTM) attain power conversion efficiency (PCE) up to 9.4% (stabilized PCE 7.2%). Furthermore, a simple HTM-free device without the PEDOT/PSS layer is demonstrated to be more stable than the full-structured device and exhibits a PCE of 7.6% (stabilized PCE 7.3%), the highest efficiency to date for an inorganic perovskite with a bandgap below 1.4 eV. This simplified device structure shows good reproducibility and stability. This work provides a possible route for fabricating low-cost, high-stability devices with competitive efficiencies.