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 (similar to 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.