Low-temperature processing of optimally polymer-wrapped α-CsPbI3 for self-powered flexible photo-detector application

Abstract

For the application of α-CsPbI₃ in optoelectronic devices, low-temperature processability and high environmental stability are critically important. Herein, we have grown a polyvinylpyrrolidone (PVP) polymer-wrapped highly stable cubic phase (α) of CsPbI₃ at low temperature (60 °C) using a single step spin coating method. The optimal quantity of PVP critically facilitates precursor diffusion to form the desired phase at low temperature and concurrently renders stability to the phase. A photo-detector using a heterostructure of CsPbI₃ and SnO₂ on a flexible substrate is demonstrated, operating over the broad wavelength range 400–700 nm in a self-powered mode. The on/off photocurrent ratio of this self-powered flexible device is >10³. The average responsivity, external quantum efficiency, and detectivity of the device are around 100 mA W⁻¹, 25%, and 10¹² Jones, respectively. The noise current of our device is 15 pA Hz^−1/2 under dark conditions (at 50 mV bias) at 117 Hz frequency. The rise/fall times of the photo-detector are found to be 5.7/6.2 μs, respectively; thus showing an ultrafast response. This self-powered flexible photo-detector shows very good stability even after 500 bending cycles.