Enhanced Power Conversion Efficiency in Tin Halide Perovskite Solar Cells with Zinc Iodide Interlayers

Optimal alignment of the energy levels can improve the performance of perovskite solar cells. In this work, we show that energy level alignment can be enhanced by a vacuum-deposited zinc iodide (ZnI2) layer inserted between tin perovskite and a C60 electron transport layer. The open-circuit voltage of FA0.75MA0.25SnI3 (FA: formamidinium; MA: methylammonium) solar cells increased by more than 0.1 V, while the power conversion efficiency increased from 10.2% to 12.8%. The shelf lifetimes of the devices are also improved. ZnI2 interlayers are also effective with other perovskites compositions, such as FASnI3 and PEA0.15FA0.85SnI3 (PEA: phenethylammonium), with their device efficiencies increasing from 6.8% to 11.6% and from 6.2% to 9.5%, respectively. The energy level diagram, derived from Kelvin probe measurements, suggests that ZnI2 interlayers reduce the band offset between perovskite and C60. As a result, the electron accumulation width in C60 is reduced, mitigating nonradiative charge carrier recombination losses and increasing the device performance.