High Efficiency Tin-Lead Mixed Halides Perovskite Solar Cells via Additive Engineering with Enhanced Electronic Properties and Stability

Perovskite solar cells (PSCs) have garnered attention worldwide as their rapid performance improvement in achieving an efficiency of more than 20% in less than a decade. This has placed the perovskite solar cells technology on par with that of silicon solar cells. In ABX₃ structure of perovskite crystals (A: monovalent organic and/or inorganic cations, B: divalent cations and X: halide anions), the tunable band gap can be accomplished by introducing tin, lead or both tin-lead cations at the B-site. This tunable property is important in achieving PSCs of desired band gap for application such as tandem solar cell devices. Tin-lead solar cells with wide range of absorption typically demonstrated band gap in the range of 1.2 to 1.3 eV makes them suitable for tandem solar cells. In this research, by adjusting the composition of metal cations in the tin-lead mixed halides perovskite, we are able to easily achieved perovskite devices with efficiencies of more than 20% with improved electronic properties and stability. The addition of the metal cations as additive has been observed to improve the surface morphology, crystallinity, charge transfer and carrier transport in tin-lead perovskite as investigated using FESEM, XRD, XPS, photo-luminescence and UV-Vis experiments. The overall improvement has been observed by incorporating two different metal cation additives; rubidium iodide and potassium iodide. Significant PCE improvement has been achieved with incorporation of either additive with the highest efficiency reached 21.04% in tin-lead mixed halides PSCs with rubidium iodide additive (Voc of 0.85 V, Jsc of 32.1 mA/cm², fill factor of 0.78). Via simple solution processing technique and spin coating method, the tin-lead mixed halides PSCs with rubidium iodide additive was able to retain 99% of its efficiency after 1 month. In terms of stability against PSCs with potassium iodide additive, the addition of rubidium iodide offers far more stable tin-lead mixed halide PSCs. As a conclusion, we are able to outline the enhancement strategy which yield remarkable efficiency of more than 20% in tin-lead mixed halides PSCs via additive engineering employing metal cations.