A Band‐Edge Potential Gradient Heterostructure to Enhance Electron Extraction Efficiency of the Electron Transport Layer in High‐Performance Perovskite Solar Cells

Abstract

As the key component in efficient perovskite solar cells, the electron transport layer (ETL) can selectively collect photogenerated charge carriers produced in perovskite absorbers and prevent the recombination of carriers at interfaces, thus ensuring a high power conversion efficiency. Compared with the conventional single‐ or dual‐layered ETLs, a gradient heterojunction (GHJ) strategy is more attractive to facilitate charge separation because the potential gradient created at an appropriately structured heterojunction can act as a driving force to regulate the electron transport toward a desired direction. Here, a SnO2/TiO2 GHJ interlayer configuration inside the ETL is reported to simultaneously achieve effective extraction and efficient transport of photoelectrons. With such an interlayer configuration, the GHJs formed at the perovskite/ETL interface act collectively to extract photogenerated electrons from the perovskite layer, while GHJs formed at the boundaries of the interconnected SnO2 and TiO2 networks throughout the entire ETL layer can extract electron from the slow electron mobility TiO2 network to the high electron mobility SnO2 network. Devices based on GHJ ETL exhibit a champion power conversion efficiency of 18.08%, which is significantly higher than that obtained from the compact TiO2 ETL constructed under the comparable conditions.

CdS as Electron Transport Layer for Low‐Hysteresis Perovskite Solar Cells

“…Additionally, the dramatically reduced j SC (only ≈9 mA cm −2 , see Table S1, Supporting Information) in comparison to the other device stacks could be due to surface recombination which is caused by unfavorable band‐bending under severe ion accumulation . In case of the TiO x ‐CdS dual layered ETL, the electron backflow can be effectively suppressed, but the advantage of using high mobility CdS cannot be exploited, because the overall electron mobility is limited by the low‐temperature compact‐TiO x layer …”

SnO2‐Based Perovskite Solar Cells: Configuration Design and Performance Improvement

“…c) Schematic diagram of the potential GHJ ETL‐based PSCs, d) schematic illustration of the separation and recombination of photogenerated charges in the devices. Reproduced with permission . Copyright 2017, Wiley‐VCH.…”

“…However, the architecture of heterojunctions in dual‐layered ETLs was planar and the high electron mobility SnO 2 cannot be fully utilized due to the upper compact TiO 2 . Inspired by Wu's work, Hou et al put forward the GHJ whose energy level structure and architecture is shown in Figure c,d, respectively . They deposited SnO 2 and TiO 2 on FTO glass, respectively, followed by the sintering step.…”

Surface Electronic Modification of Perovskite Thin Film with Water‐Resistant Electron Delocalized Molecules for Stable and Efficient Photovoltaics

“…[1][2][3][4][5][6] Although the PCE of perovskite solar cells soared to a high value of 22.1% close to single crystalline-silicon-based solar cells, [7] the instability of perovskite material still hinders the development of large-area module and further commercialization. [1][2][3][4][5][6] Although the PCE of perovskite solar cells soared to a high value of 22.1% close to single crystalline-silicon-based solar cells, [7] the instability of perovskite material still hinders the development of large-area module and further commercialization.…”

“…Among various molecules, thiophene derivatives enable the electron-rich conjugated π system, which consist of four 2p orbital electrons from carbon atoms and two lone electron pairs from sulfur atom. [1][2][3][4][5][6] Although the PCE of perovskite solar cells soared to a high value of 22.1% close to single crystalline-silicon-based solar cells, [7] the instability of perovskite material still hinders the development of large-area module and further commercialization. [28] Moreover, unlike siloxanes and amines, thiophenes can be directly coordinated to the lead atom by the lone pair of electrons offered by the sulfur atom, which may be directly interacted with the valance band of perovskite.…”