Zirconium Doping to Enable High-Efficiency and Stable CsPbI₂Br All-Inorganic Perovskite Solar Cells

All-inorganic wide-bandgap perovskite CsPbI₂Br has attracted much attention because of its inherent thermal stability and ideal bandgap for the front subcell of tandem solar cells (TSCs). However, the low power conversion efficiency (PCE) and poor moisture stability of CsPbI₂Br still restrict its future commercialization. Herein, zirconium tetrachloride (ZrCl₄) was doped into CsPbI₂Br films to modulate the crystal growth and improve the film quality. The partial substitution of the B-site Pb²⁺ of CsPbI₂Br with Zr⁴⁺ suppresses the unwanted phase conversion from the crystallized black α-phase to the δ-phase, resulting in improved phase stability. Consequently, the humidity and thermal stability of the film are greatly improved. Additionally, the incorporation of ZrCl₄ suppresses nonradiative recombination and forms a matched energy-level alignment with the hole-transport layer (Spiro-OMeTAD). Benefiting from these features, the ZrCl₄-doped CsPbI₂Br perovskite solar cell (PSC) shows an outstanding efficiency of 16.60% with a high open-circuit voltage of 1.29 V. The unencapsulated devices simultaneously show excellent humidity and thermal stability, retaining over 91% of PCE_initial after 1000 h of aging in ambient air conditions and 92% PCE_initial after 500 h of continuous heating at 85 °C in a nitrogen environment, respectively. Furthermore, ZrCl₄-doped CsPbI₂Br was employed as the front subcell of perovskite/organic TSCs and achieved a remarkable PCE of 19.42%, showing great potential for highly efficient and stable TSCs.