Vapor-deposited all inorganic CsPbBr3 thin films and interface modification with C8-BTBT for high performance photodetector

All inorganic perovskites like CsPbBr3 have attracted rising attention and are considered as promising candidates for optoelectronic devices. Here we fabricated CsPbBr3 films by co-evaporation. The as-deposited and low temperature (below 300 degrees C) annealed films are in a mixture phase of CsPbBr3 and CsPb2Br5. After 400 degrees C annealing in ambient air, the CsPbBr3 phase becomes dominant with a good crystal structure and less defects. Then, 2,7-diocty[1]benzothieno-[3,2-b]benzothiophen (C8-BTBT) was deposited on the CsPbBr3 film layer-by-layer to investigate the interface electronic structure with X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). As C8-BTBT was deposited, p-doping effect was observed at the surface of CsPbBr3 by the interface energy level alignment. At the same time, we also observed a chemical reaction at the interface and a small amount of lead sulfite might be formed. CsPbBr3 based photodetectors with or without C8-BTBT modified layer were also fabricated and studied. It was found that the photocurrent of the detectors with an additional C8-BTBT layer was about two orders of magnitude higher than that without C8-BTBT layer. The responsivities and response time are also improved with C8-BTBT. We attribute the improvement of photoelectronic properties to the interface energy level adjustment by the C8-BTBT. These results highlight the potential of C8-BTBT as a modified layer for inorganic perovskite optoelectronic devices.