Effect of surface recombination in high performance white-light CH₃NH₃PbI₃ single crystal photodetectors

Methylammonium lead iodide (CH₃NH₃PbI₃), with the organic-inorganic hybrid perovskite (OIHP) structure, has gained tremendous research interest due to its excellent photo-electron conversion ability in the application of photovoltaics. Despite its solution processed polycrystalline thin film form in solar cells, the single crystalline counterpart may offer some incredibly novel optoelectronic functionalities. In this work, a sizable (>5 mm) and high quality CH₃NH₃PbI₃ single crystal has been synthesized by the inverse temperature crystallization method, and a white-light photodetector of the structure glass/ITO/Ga/ CH₃NH₃PbI₃/Au was fabricated. Overbroad photo-excitation intensities ranging from 0.1 mW/cm² to 100 mW/cm² using a sun-light simulator, the on-off ratio is tunable in a wide-range from 65 to 2250 at zero bias voltage. The responsivity (R) and detectivity (D*) are 36.2 mA/W and 2.68×10¹¹ Jones respectively at a weak white-light intensity such as 0.1 mW/cm². Both the photodetective parameters decrease with the increase of the illumination intensity. Based on impedance spectra obtained at working condition and light intensity dependent J_sc measurements, the surface trap-assist recombination may play a dominating role. The corresponding lifetime (τ_surf) and resistance (R_{surf_trap}) exhibit fast decays at higher illumination intensities. This fundamental study may pave the way for exploring the contribution of the surface trap-assist recombination in the CH₃NH₃PbI₃ single crystal based photodetector. We believe it is applicable for integration in micro-photonics for sensitive and weak white-light photo-detection.