Schottky/p‐n Cascade Heterojunction Constructed by Intentional n‐Type Doping Perovskite Toward Efficient Electron Layer‐Free Perovskite Solar Cells

Abstract

Electron transport layer (ETL)‐free perovskite solar cells (PSCs) are getting much more attention with their simpler structure and potentially low cost as well as higher stability. However, the elimination of ETL (such as TiO2) with intrinsically deep valance band level leads to the absence of the hole blocking mechanism and thus serious charge recombination at the FTO/perovskite interface compared with ETL‐based devices. An interface band bending associated built‐in electric field is an essential driving force of charge separation. Here, by intentional polarity tailoring of perovskite via incorporation of Sb as a shallow donor, ETL‐free PSCs with optimized energy level alignment both at the front and rear interfaces are constructed, resulting in an enhanced built‐in electric field and thus efficient majority carrier collection and minority blocking as well as reduced interfacial charge recombination at both interfaces. Device simulation calculations also confirm the importance of polarity control for device performance improvement. The effect of doping on the perovskite films properties and device performance are systematically demonstrated. Correspondingly, ETL‐free PSCs with a champion power conversion efficiency of 12.62% is achieved.

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

“…To probe the electron transfer and carrier separation processes at the FTO/perovskite interface, steady-state PL spectroscopy was carried out. Their finding is in well consistent with the results reported by Huang et al [54] The kinetics of the luminescence of perovskite films in the nanosecond time range has also been studied. Similar to the PL quenching degree of the perovskite film deposited on TiO 2 , ≈70% PL quenching can be observed when the perovskite was deposited on FTO, demonstrating the FTO as an efficient electron extraction cathode to ensure high efficient ETL-free device.…”

“…[83] For the first time, the effect of the property of the HTL on the performance of the ETL-free PSCs was emphasized. [54] The resulted ETL-free device with a Schottky/p-n cascade heterojunction presents a much higher efficiency than that of the control device with pristine perovskite. [54] The resulted ETL-free device with a Schottky/p-n cascade heterojunction presents a much higher efficiency than that of the control device with pristine perovskite.…”

“…Specific interface band structure requires photoelectron characterization. [54] Thus, to improve the performance of such device, the band bending at both of the two interfaces should be considered as a whole. [131] The observed downward band bending in the perovskite (Figure 10c) suggests the n-type nature of the prepared MAPbI 3 and the work function of perovskite is smaller than ITO.…”

“…The KPFM measurement was conducted to confirm the p-n heterojunction and depletion field at the spiro-MeOTAD/perovskite interface (Figure 15d), as demonstrated by the local CPD distribution between tip and sample across the spiro-MeOTAD and perovskite surface (Figure 15e,f). The enhanced built-in electric field thus efficient majority carrier collection and minority blocking as well as reduced interfacial charge recombination at both interfaces (Figure 10e,f) [54] leads to ETL-free PSCs with a Schottky/p-n cascade heterojunction that achieves a maximum efficiency of 12.62%, demonstrating new solutions to further enhance the device performance of ETL-free PSCs. [134] They found that a decreased work function of FTO (4.6-4.0 eV) can suppress the recombination at the FTO/perovskite interface and greatly improve the efficiency.…”

“…Perovskite films with a large grain size exceeding 12 µm can be achieved by adopting a 1.25 m concentration of perovskite precursor. [54] Copyright 2018, Wiley-VCH. Energy Mater.…”