Partha Pratim Ray
Jadavpur University, India
Title: Piezo response of defects mediated Methyl Ammonium Lead Iodide (MAPbI3)
Biography
Biography: Partha Pratim Ray
Abstract
Formation of lattice defects (point defects/dislocations/grain boundaries) is an unavoidable phenomenon which is associated with almost all synthesis procedures following fast formation kinetics. Therefore a polycrystalline thin film of hybrid perovskite developed for a solar cell invariably contains lattice defects. Similarly in a systematic fashion using ball mill grinding technique we have synthesized perovskite material, Methylammonium lead iodide (MAPbI3) with different degrees of crystal defects as probed by positron annihilation spectroscopy (PAS) and utilized to fabricate flexible piezoelectric nanogenerators (FPENGs). Five sets of MAPbI3 samples are prepared by ball mill grinding procedure with different grinding time (15m, 30m, 60m, 90m and 120m). The formation and morphology of MAPbI3 is confirmed from their powder XRD pattern and field emission scanning electron microscopy (FESEM) images. The optical band gaps (1.63 eV) of all the samples are calculated from their absorption onset at 760 nm. The x-ray diffraction pattern suggests the formation of tetragonal crystal phase. We have demonstrated that at room temperature the lattice defects play the pivotal role in governing the ionic polarization from temperature dependent dc conductivity measurement and establish one-to-one correlation with the lattice defects as probed by PAS, which in principle governs the piezo-effect in MAPbI3. Here, we have shown that lattice defect mediated ionic polarization significantly changes VOC, but ISC remains almost same for all the samples as ISC has its origin on the value of piezoelectric constant and elastic modulus of the material. The best device performance is exhibited by maximum defect containing sample (30m) having significant amount of Pb2+ defects. A device fabricated with 5 wt % PDMS composite produces piezo-voltage (>100V) with a maximum power density of 0.3 mW/cm3 and can illuminate commercially available 30 blue light emitting diodes.
