Development of an In-situ Defects Measurement to Investigate the Degradation in Multiple-ion Composite Perovskite Solar Cells

Description

Solution derived hybrid halide perovskite is an emerging material for opto-electronic applications. The power conversion efficiency (PCE) of single-junction perovskite solar cells (PVSCs) has already achieved 25.5%, exceeding that in multi-crystalline silicon solar cells. Several research groups have also demonstrated superb device stability in MAPbI3 based PVSCs. However, as the silicon-based technology has already been well established with largescale production and low-cost, it is challenging for the perovskites to compete with silicon in the existing photovoltaic market. On the other hand, due to the ease of fabrication and high tunability of opto-electronic properties, perovskites have great potential for developing highefficiency and low-cost multi-junction photovoltaic devices. However, both large (>1.8eV) and small (<1.2eV) bandgap perovskites fabricated with multiple cations and anions are stillsuffered from instability issues. Fundamentally, the ion dissociation process under various operation conditions in multiple-ion composite perovskites is still not clear. There is also lack of viable technique to effectively suppress the degradation. Therefore, it is of the utmost importance to understand the intrinsic degradation mechanism in multiple-ion composite perovskites and develop approaches to enhance the material stability. In this proposed research, we are aiming at developing an in-situ highly sensitive external quantum efficiency (s-EQE) technique to determine the defect evolution during the multipleion composite PVSCs degradation. Particularly, the in-situ technique to be developed can detect defects during the device operation with ultra-high sensitivity, it enables the detection of extremely small photocurrent generated from defect states even at the early stage of device operation. Technically, we will consolidate the s-EQE method by comparing with other defect measurement approaches, such as thermal admittance spectroscopy(TAS). The techniques willbe verified by measuring a series of perovskite materials with controlled defect densities and energies. Scientifically, we will apply the technique to investigate the impact of different operation conditions on defects growth in wide-bandgap(e.g. FAxMA1-xPb(IyBr1-y)3) and lowbandgap (e.g. FAxMAyCs1-x-yPbzSn1-zI3) perovskites. Notably, PVSCs performance and stability are very sensitive to the composition of ions, we will conduct systematic studies to investigate the correlation between the degradation and the growth of defect with different compositions. In addition, we will further apply the technique to investigate the effect of different properties in passivation molecules (e.g. Lewis acid and base) on the growth of defect in perovskites. Ultimately, the degradation mechanism in multiple-ion composite perovskites can be identified and can bring insights into developing strategies to improve the wide and low bandgap PVSCs stability.