Optimized perovskite active layer morphologies and crystallization by doping cesium iodide for high-performance bulk heterojunction solar cells and X-ray detectors

Organic-inorganic hybrid methylammonium lead iodide perovskite (MAPbI(3)) has attracted widespread attention for its potential use in a range of optoelectronic devices. In this paper, we describe the fabrication of inverted-type perovskite/fullerene planar heterojunction perovskite solar cells and X-ray detectors where a small amount of cesium iodide (CsI) was added to the MAPbI(3) precursor solution. The appearance and crystal structure of the constructed perovskite active layer were carefully studied by microscope and X-ray diffraction measurements, respectively. The results reveal that the CsI additive can control the size and aggregation behavior of the perovskite crystals, helping to form a smoother perovskite film. Thus, the constructed perovskite solar cell with its Cs(0.1)MA(0.9)PbI(3) active layer (AC) revealed a power conversion efficiency (PCE) of 11.16 +/- 0.13%, which is a significant improvement over conventional planar heterojunction devices that use pristine MAPbI(3) AC (PCE 9.12 +/- 0.11%). We also fabricated an X-ray detector using the same Cs(0.1)MA(0.9)PbI(3), this achieved a maximum sensitivity of 3.26 mA/Gy cm(2). Density functional theory calculations investigate the origin of the enhancement of device performance characteristics. Interestingly, the results show that perovskite surfaces constructed with a suitable amount of CsI can effectively enhance charge extraction and reduce charge carrier recombination. This work provides an efficient way to improve carrier transfer, which will inspire other perovskites optoelectronic applications.