| 초록 |
Organic–inorganic lead tribromide perovskites, with their wide bandgaps, are highly regarded as potential candidates for the topmost cell in a tandem cell or in a photocatalytic system. Herein, we report on the effects of cesium incorporation into formamidinium lead tribromide (CH(NH2)2PbBr3 = FAPbBr3) perovskite films on the morphologies, crystal structures, orientations, photophysical properties, and their photovoltaic performance. The partial incorporation of CsBr into a FAPbBr3 film inhibits the PbBr2 impurity phase and tunes crystal-lattice interactions, resulting in a crystal system with preferred orientation. A planar-configured photovoltaic device assembled with FAPbBr3 loaded with 8% Cs (Cs0.08FA0.92PbBr3) exhibited an optimum PCE (power conversion efficiency) of 8.56% with a Voc of 1.516 V, which is higher than the PCE 7.07% and Voc 1.428 V of the FAPbBr3 device. Photoluminescence-intensity and temporal-imaging experiments were conducted by laser scanning confocal time-resolved microscopy (LCTM), which revealed that CsBr incorporation into a FAPbBr3 film significantly suppresses the non-radiative recombination pathways. Also, the wide-area photoluminescence imaging demonstrated that the spatial distribution of photoluminescence was homogeneous in the Cs-incorporated FAPbBr3 films. It is visualized that the incorporation of CsBr in FAPbBr3 directly affects the bulk defect and photoluminescence properties, which provides evidence that Cs ions surely alleviate the segregation and aggregation of ions in the perovskite film. Notably, the Cs0.08FA0.92PbBr3 film, with a carrier lifetime of about 270 ns, exhibited a 1.37-fold longer radiative recombination time than that (210 ns) observed for the FAPbBr3 film. Furthermore, aging experiments without encapsulation under intrinsic (in air for 2000 h) and extrinsic (65 °C and 65% RH for 500 h) conditions reveal that the Cs0.08FA0.92PbBr3 device is more robust than the FAPbBr3 device. |
