Capacitance Spectroscopy of Perovskite Solar Cells: Time vs Frequency Domain Methods
Nisheka Anadkat a, Shruti Shukla a, K L Narasimhan a, Sushobhan Avasthi a
a Centre for Nanoscience and Engineering, Indian Institute of Science, Bangalore 560012, India
Proceedings of Device Physics Characterization and Interpretation in Perovskite and Organic Materials (DEPERO)
València, Spain, 2023 October 3rd - 5th
Organizers: Sandheep Ravishankar, Juan Bisquert and Evelyne Knapp
Oral, Nisheka Anadkat, presentation 014
Publication date: 14th September 2023

Metal halide perovskites have gained immense attention from the photovoltaic research community due to its phenomenal optoelectronic properties that have skyrocketed the power conversion efficiency (PCE) of perovskite solar cells to 25.7% over the past decades [1]. The research scientists have endeavoured to provide insights on the device physics of perovskite solar cells (PSC). Special attention is required to comprehend the details governing the role of defects and its properties on the performance of PSCs. Defects in the bandgap or at its interfaces in perovskite elicit anomalous behaviour of the performance as it acts as a recombination centres and ion migration sites. To probe the defect properties, we have explored capacitance measurement approaches such as capacitance-voltage (CV), capacitance-frequency (C-f), thermal admittance spectroscopy (TAS) and deep-level transient spectroscopy (DLTS) to quantify the defect properties in CH3NH3PbI3 based perovskite solar cells [2,3]. The steady-state capacitance vs frequency scans at different temperatures (C-f-T) from 150K to 320K reveal two prominent capacitance steps at low frequency-high temperature (LF-HT) and high frequency-low temperature (HF-LT). The voltage-dependent (C-f-T) allows to distinguish the surface and bulk defects. The low frequency capacitance shows prominent increase in capacitance with increase in temperature due to ionic contribution. The prominent defects were observed with activation energies of 0.16eV and 0.54eV from the band edges. These activation energies are influenced by charge transport layers, hence, capacitance contribution due to perovskite and charge transport layers must be separated. However, the nature of traps can be determined using transient capacitance technique. The capacitance transient spectra at different temperature (C-t-T) from 200K to 350K shows anomalous behaviour such as capacitance increases initially with temperature and then decreases above 320K possibly due to perovskite phase transition. DLTS measurements reveal a dominant defect level with activation energy of 0.56eV. These findings show qualitative agreement with the theoretical values using DFT calculations reported in the literature. Frequency domain and time domain measurements collectively provide complete information about defects. Eventually, we provide comprehensive insights into charge accumulation, band bending and capture and emission process using band diagrams.

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