Study of compositional stability and related optical properties of perovskite CH(3)NH(3)PbBr(3)films fabricated via two-step sol-gel process using weakly coordinating isopropanol solvent

摘要

Compositional stability of perovskites is crucial for perovskite solar cells (PSCs) application because of directly affecting the performance of PSCs. Highly crystallized perovskite MAPbBr(3)(MA = CH3NH3) with micronscale crystallites are usually fabricated via the one-step sol-gel process that uses strongly coordinating organic solvents. The two-step sol-gel process using weakly coordinating organic solvent is rarely used to fabricate MAPbBr(3)films with relatively small crystallites. However, the two-step sol-gel process is preferred to fabricate PSCs because the residual PbBr(2)can prevent the direct contact between electron- and hole-transporting layers. Thus in this work, perovskite MAPbBr(3)films are fabricated via two-step sol-gel process using weakly coordinating isopropanol solvent. The compositional stability in dry ambient air and related optical properties of the films are intensively studied by a technique of post-annealing. A compositional transition from MAPbBr(3)to PbBr(2)occurs with increase of post-annealing temperature (T-pa). The product PbBr(2)begins to form in the MAPbBr(3)films at approximately 130 degrees C T-pa, and MAPbBr(3)is fully thermally degraded to PbBr(2)at 170 degrees C T-pa. The compositional stability of the films in dry air is inherently determined by instable organic cations (MA)(+)and small electronegativity of Br-. The perovskite film initially shows a redshifted and then a blueshifted optical absorption edge with increase of T-pa, which is due to the decrease in film tensile stress and to the enhancement in thermal degradation to PbBr2, respectively. The increase in number of PbBr(2)particles and defects in the films remarkably reduces the intensity of the green emission of MAPbBr(3).