Systematic investigation of LiI incorporation effects into MAPbI₃-precursors for enhanced photodetection applications

The incorporation of Alkali metals into metal halide perovskites (MHPS) has recently been examined as a viable technique for improving optoelectronic performance. However, the suggested role of the alkali metals is mainly limited to surface passivation, and the doping action in the semiconductor material is rarely considered. Here, the mechanism of lithium doping in a solution-processed methylammonium Lead Iodide (MAPbI₃) has been investigated via the addition of LiI in varying molar concentrations. Advanced characterization techniques such as X-ray photoelectron spectroscopies (XPS), Scanning electron microscopy (SEM), Energy dispersive Spectroscopy (EDS), Ultraviolet-visible spectrophotometry, and Photoluminescence spectrofluorometery were employed in the study. Lithium doping in MAPbI₃ has been shown to have several beneficial effects, including suppressing carrier traps and acting as a donor. This means that lithium ions not only reside on the surface of the material but also penetrate the lattice structure. This study has demonstrated that lithium doping can lead to lattice expansions in perovskite crystals and generate free electrons, which occupy interstitial sites and fill trap states. As a result, photocarrier trapping is suppressed, and the extraction of charge carriers becomes more efficient. These findings are supported by experimental techniques such as XRD spectra and photoluminescence measurements, which provide evidence of structural changes and enhanced radiative recombination processes in lithium-doped MAPbI₃ films. The study involves an in-depth evaluation of the performance of an optimized vertical structure photodetector with FTO upper and lower electrodes. Incident light directed via the transparent top and bottom FTO electrodes, traverse a structure composed of a hole transport layer (HTL), hole blocking layer (HBL), and electron transport layer (ETL), with dual absorber layers interposed between them. It has been discovered that adding LiI can improve perovskite material crystallinity, light absorption, and overall optoelectronic performance of the constructed devices.