High Efficiency Inorganic Perovskite Solar Cells Based On Low Trap Density and High Carrier Mobility CsPbI3 Films

Abstract

<p>Inorganic perovskite CsPbI₃ has exhibited promising performance in single-junction solar cells, but the grain boundaries (GBs) in its film cause the formation of the defects with deep energy levels (such as iodide vacancy (<em>V</em>_I)) and impede the transport of carriers, worsening the efficiency and stability of the solar cells. Here, a CsPbI₃ precursor is devised with thiophenol series ligands (TP-ligands) containing both SH and π-conjugated molecules. The strong interaction between the SH group (Lewis base) and PbI₂ (Lewis acid) suppresses the formation of PbI₄²⁻ in perovskite solution, thus suppressing the formation of <em>V</em>_I in the film accordingly. The terminal groups, such as -F and -NH₂, are employed to achieve an appropriate evaporation speed of the ligands and prevent the oxidation of the thiophenol group, then a high-quality perovskite film with low trap density is obtained. In addition, the functional group π-conjugated molecules provide additional carrier transmission channels at the GBs to increase carrier mobility, which facilitates the exciton separation and prolongs the charge lifetime. The CsPbI₃ solar cell shows a considerable power conversion efficiency of 20.1% with an open-current voltage of 1.18 V and a high fill factor of 83.5% and excellent working stability.<br></p>