Publication date: 2nd November 2020
Abstract: Additive Engineering is a key approach to achieve high performance hybrid perovskite solar cells (PSCs) by passivating the bulk defects. However, a clear understanding about the nature of defects and which charge carrier (either hole or electron or both) gets trapped in the defect states, is still required. Herein, we present a comparative study on the estimation of charge transport length scale (L) in pristine versus passivated MAPbI3-based PSC via scanning photocurrent microscopy (SPM). The SPM study suggested an improved L and degree of ambipolarity of photo-generated charge carriers (electron and hole) in passivated as compared to pristine MAPbI3-based PSCs. These results were found to be correlated with frequency dependent photocurrent measurement, which shows that the relaxation time of the charge carrier is relatively lower in passivated MAPbI3-based PSCs. This mechanism could be explained by trap-assisted recombination, where trap states are induced by ion migration in halide perovskite films. Furthermore, passivation of traps showed an increased degree of ambipolarity in the perovskite semiconductor thin film and provides an insight about charge carrier trapping in the pristine MAPbI3-based PSC.
Keywords: MAPbI3, defects, scanning photocurrent microscopy, dielectric relaxation time constant, degree of ambipolarity.
This work was also partially supported by the UKRI Global Challenge Research Fund project, SUNRISE (EP/P032591/ 1). The authors also acknowledge the support of National Centre for Photovoltaic Research and Education (NCPRE) for the deposition facility and characterization. We also acknowledge IRCC central facility IIT Bombay for XPS and dielectric constant measurement.
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