An Approach to Quantify the Negative Capacitance Features in a Triple‐Cation based Perovskite Solar Cells

Abstract

Understanding the device kinetics occurring in the bulk and charge selective layers is vital for optimizing the performance of perovskite solar cells (PSCs) and their development. We studied planar PSCs with and without hole transport layer (HTL) and measured hysteresis free power conversion efficiency of 16.23% with poly(3-hexylthiophene) [P3HT] as HTL, while the PSCs without HTL showed significant hysteresis. We investigated a comprehensive electrical response of the PSCs. The bias-dependent electrochemical impedance spectroscopy (EIS) revealed the appearance of the negative capacitance in the low-frequency regime. The modification of the low-frequency PSCs response accompanied by a further decrease in recombination resistance is due to the interfacial interactions between the migrating ions and the metal contact. The doped and undoped P3HT layers impeded this interaction which explains the absence of the negative capacitance at lower applied voltages. Our investigation provides an understanding of the physical processes behind the negative capacitance.

Negative Transient Spikes in Halide Perovskites

“…In the field of halide perovskite solar cells, the presence of negative capacitances has featured strongly since the early investigations, ,,− and different explanations have been adopted to explain such features, such as the physical surface polarization model (SPM), , the changing environment of ions when their occupation at the double layer is modified by the applied voltage, ,, and the modulation of electron/hole conduction or recombination currents. ,,− The general idea behind most of these models is based on the combination of ionic and electronic phenomena that robustly determine the dynamic response. There is an ionic reorganization determined by a slow time constant that influences the electronic current.…”

Impact of Polymeric Hole‐Selective Layers on Chemical Inductance in Inverted Perovskite Solar Cells

“…The high‐frequency capacitance is attributed to the result of the series resistance imposed by the contact electrodes. The capacitance produced in the midfrequency range corresponds to the dielectric relaxation in the perovskite layer and is expressed by the geometrical capacitance [ 29,60 ] per unit area (). The constant value of capacitance, which is temperature independent at the IF region suggests the stable geometrical capacitance associated with the perovskite layer.…”

“…28 We also reported that the low-frequency negative capacitance feature in n-i-p type PSCs is intimately related to the interfacial interactions of migrating ions with metallic contact and redistribution occurring at the perovskite interfaces. 29 The negative capacitance feature is not limited to the n-i-p type PSCs only but has been also observed in p-i-n based architects.…”

“…Triple cation perovskite [Cs 0.1 (FA 0.9 MA 0.1 ) 0.9 Pb(I 0.9 Br 0.1 ) 3 ] was deposited according to our previous reports. [ 29 ] In the case of PTAA based solar cells, 60 μL of DMSO was dropped on the PTAA layer just before the perovskite deposition. The PC 60 BM thin film as an electron transport layer was spin coated (15 mg mL −1 in CB) at 1200 rpm for 30 s over the perovskite active layer.…”

“…[ 28 ] We also reported that the low‐frequency negative capacitance feature in n‐i‐p type PSCs is intimately related to the interfacial interactions of migrating ions with metallic contact and redistribution occurring at the perovskite interfaces. [ 29 ] The negative capacitance feature is not limited to the n‐i‐p type PSCs only but has been also observed in p‐i‐n based architects. However, the surface recombination at the perovskite/HTL interface has received less academic interest in the p‐i‐n type PSCs and how the choice of HTLs affects the device performance has not been comprehensively unraveled.…”