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

For the application of alpha-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 (alpha) of CsPbI3 at low temperature (60 degrees 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 >10(3). The average responsivity, external quantum efficiency, and detectivity of the device are around 100 mA W-1, 25%, and 10(12) 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 mu s, respectively; thus showing an ultrafast response. This self-powered flexible photo-detector shows very good stability even after 500 bending cycles.