Lattice relaxation effect in CsxMA(1-x)PbBr3 single crystal to enhance optoelectronic performance of perovskite photodetectors

Abstract Single crystal (SC) MAPbBr3 perovskite is regarded as a promising material to fabricate high-performance photodetectors (PDs) due to its impressive optoelectronic properties and good chemical stability. Cs+ doping has been proved to be an effective method to significantly improve the optoelectronic properties of MAPbBr3 SC. However, the intrinsic effect of Cs+ on the crystal structure is still unclear. Herein, we grew a series CsxMA(1-x)PbBr3 SCs. X-ray rocking curves (XRC) of CsxMA(1-x)PbBr3 SCs prove that appropriate Cs-doping concentration could reduce defect density effectively. X-ray photoelectron spectroscopy (XPS) measurements indicate that Cs-doping enhances the atoms interaction in CsxMA(1-x)PbBr3 lattice due to isoelectronic impurity effect. Single-crystal PDs were fabricated to compare the optoelectronic properties of MAPbBr3 SCs with different Cs-doping concentration, and the 2% Cs-doped CsxMA(1-x)PbBr3 PD shows the optimum performance. Density functional theory (DFT) calculations demonstrate that Cs-doping leads to lattice relaxation effect which is benefit to reduce trap density of CsxMA(1-x)PbBr3 SCs. The Pb-6p level of CsxMA(1-x)PbBr3 slightly shifts to lower energy region compared with MAPbBr3, resulting in the decrease of band gap of CsxMA(1-x)PbBr3.