Surface Evolution and Fractal Dimensions of CH3NH3PbI3-XClX Thin Films and its Photovoltaic Performance

Abstract

We fabricated the CH₃NH₃PbI_3-XCl_X perovskite crystalline films by solution processed method in air and nitrogen ambience to investigate the impact of the growth conditions on surface morphology and interface properties of the films. The surface morphology of CH₃NH₃PbI_3-XCl_X thin films are captured by scanning electron microscopy (SEM) and fractal analysis is performed on SEM micrographs. The value of fractal dimension/hurst exponent is found to be larger/smaller in N₂ environment as comparison to open air environment. The greater value of fractal dimension is corresponding to larger surface jaggedness which plays a crucial role for improving the interface between the perovskite and hole transportation layer. Furthermore, this analytical prediction is confirmed by photovoltaic devices fabricated on these films and observed a 60% enhancement in power conversion efficiency (PCE)  of N₂ environment based thin films as compare to open air processed films. This may be due to the formation of compact and voids free perovskite self-affine fractal surfaces under nitrogen environment as compare to open air environment. Our findings represent a step forward to the realization of the peculiar morphological behaviour of the mixed halide perovskite fabricated in different environmental conditions.