Influence of Charge Transport Layers on Open-Circuit Voltage and Hysteresis in Perovskite Solar Cells

Abstract

Perovskite materials are becoming a major player for the future energy scenario. In only a few years, they have demonstrated extraordinary capabilities for optoelectronic applications, promising the highest efficiency at the lowest cost. However, despite the numerous studies reported in the literature, the photophysical behavior and device physics for this new technology remain unclear. Here we reveal fundamental insights into the operation mechanism of the state-of-the-art perovskite solar cells, shedding light on the origins of the opencircuit potential and the hysteretic behavior. HIGHLIGHTS The interplay between the chargetransporting layers and opencircuit potentialThe nature of the contacts: a critical factor for the interfacial charge accumulationThe quasi-Fermi level splitting and recombination inside the perovskite rules the V OC The electric field is not the dominant extraction mechanism for the photocarriers Ravishankar et al., SUMMARYPerovskite materials have experienced an impressive improvement in photovoltaic performance due to their unique combination of optoelectronic properties. Their remarkable progression, facilitated by the use of different device architectures, compositional engineering, and processing methodologies, contrasts with the lack of understanding of the materials properties and interface phenomena. Here we directly target the interplay between the charge-transporting layers (CTLs) and open-circuit potential (V OC ) in the operation mechanism of the state-of-the-art CH 3 NH 3 PbI 3 solar cells. Our results suggest that the V OC is controlled by the splitting of quasi-Fermi levels and recombination inside the perovskite, rather than being governed by any internal electric field established by the difference in the CTL work functions. In addition, we provide novel insights into the hysteretic origin in perovskite solar cells, identifying the nature of the contacts as a critical factor in defining the charge accumulation at its interface, leading to either ionic, electronic, or mixed ionic-electronic accumulation.

Elucidating the Impact of Charge Selective Contact in Halide Perovskite through Impedance Spectroscopy

“…In LF region (20 Hz-1 kHz) capacitance decreases with frequency and is temperature dependent. [44][45][46][47] The devices fabricated with mixed perovskite showed similar trend, suggesting low frequency behavior is related to interfacial properties rather than bulk. The stable plateau in IF range corresponds to dielectric relaxation in the perovskites layer and determined by the geometrical capacitance per unit area C g = εε 0 /L, where ε is dielectric constant of perovskite, ε 0 is the vacuum permittivity, and L is the layer thickness.…”

Simple, Robust, and Going More Efficient: Recent Advance on Electron Transport Layer‐Free Perovskite Solar Cells

“…[58] They found that TiO 2 compact layers derived from atomic layer deposition (ALD) contain less pinholes than layers obtained by spin coating and spray pyrolysis methods, thus the ALD-based TiO 2 layer functions as a vigorous hole-blocking layer in PSCs as it offers a large shunt resistance which enables a high PCE of 12.56%. 2019, 9,1900248 [41] www.advancedsciencenews.com in the early stages of PSCs research, the growth process of the perovskite film was not well optimized as they are today, as evidenced by the hard-to-get PCE of 12.56% based on ALD-TiO 2 layer with extremely complex and expensive preparation methods at that time. Particularly, Adv.…”

“…[41,70] Using the potential profiling, Xiao et al compared three types of cells made of different ETLs but otherwise having an identical device structure (Figure 3a). [41,70] Using the potential profiling, Xiao et al compared three types of cells made of different ETLs but otherwise having an identical device structure (Figure 3a).…”

“…The electric-field ratio between the ETL/perovskite and perovskite/HTL interfaces increased as follows: FTO < SnO 2 − ETL < SnO 2 + SAM (C 60 self-assembled monolayer). [41] Their work suggests that the V oc is dominated by the splitting of quasi-Fermi levels and recombination in the perovskite bulk (Figure 3d), rather than being governed by any built-in electric field created by the CTL work function difference, which indicates that the Adv. The further improvements with adding a SAM is a result of the defect passivation at the ETL/perovskite interface, and thus, improvement of the junction quality ( Figure 3b).…”

“…[86] The I-V respond of the TiO 2 /spiro-MeOTAD heterojunction based device (Figure 14a) suggests that such a heterojunction has well rectifying characteristics which can avoid the device from being short circuited. [41,86] Further experiment suggests that when coverage decreases, the device performance drops significantly. Huang et al demonstrated systematically the crucial role of high perovskite coverage in high-efficiency ETL-free PSCs from an energy band and equivalent circuit point of view.…”