Study on the defect density of states in light soaking effect enhanced performance of perovskite solar cells

Abstract

The light soaking phenomenon, in chlorine-based mixed halide perovskite solar cells (PSC) with p-i-n configuration, is studied. Due to light soaking, the solar cells have shown improved open circuit voltage, fill factor (FF), and power conversion efficiency without much change in short circuit current. The devices have returned to their original state upon extended exposure to dark conditions. Capacitance spectroscopy is used to understand the effect of light soaking on various photovoltaic parameters. The observed increase of capacitance value with light soaking in the low frequency region of the capacitance-frequency (C-F) plot is elucidated, as the coupled effect of electronic and ionic processes involving defects. The decrement in the mid-frequency capacitance is attributed to an increase in the width of the depletion region which eventually facilitated the improvement in open circuit voltage and FF. Defect densities, and its distribution in the energy space, are deduced before and after light soaking. The defects density of states of PSC studied are found to reduce from 10 16 to 10 15 eV −1 cm −3 , with a Gaussian distribution, and having a peak energy shift from 0.27 to 0.26 eV.

Elimination of Light-Soaking Effect in Hysteresis-Free Perovskite Solar Cells by Interfacial Modification

“…The high frequency range is the carrier freeze region. 52 As shown in Figure 7, at high frequency, the capacitance values are substantially coincident and do not change with illumination, indicating the intrinsic perovskite properties. There are also no major changes at the intermediate frequency range.…”

“…The C–f diagram is usually divided into 3 parts. , The low frequency region capacitance corresponds to the electron and possible ion accumulation process and involves the defect state at the interface between perovskite and contact layers. , The intermediate frequency capacitive response of the forming platform is related to the intrinsic dielectric polarization of perovskite. The high frequency range is the carrier freeze region . As shown in Figure , at high frequency, the capacitance values are substantially coincident and do not change with illumination, indicating the intrinsic perovskite properties.…”

Photoinduced Dynamic Defects Responsible for the Giant, Reversible, and Bidirectional Light-Soaking Effect in Perovskite Solar Cells

“…This indicates that the LSE is somehow an intrinsic property of bulk LHPs. Using capacitance spectroscopy, Srivastava et al 27 showed that the defect density in PSC reduced from 10 16 to 10 15 cm −3 after light soaking, directly indicating that point defects are involved in LSE.…”

Alternating Current Techniques for a Better Understanding of Photoelectrocatalysts

“…Figure a is the capacitance–frequency graph (C–F). It shows three different regions such as (a) high frequency (HF), (b) midfrequency (MF), and low frequency (LF), where capacitance at low frequency is increasing with respect to light illumination as the surface is populated increasing with the charged species that resulted by the action of SS …”