Band Alignment Engineering Towards High Efficiency Carbon‐Based Inorganic Planar CsPbIBr₂ Perovskite Solar Cells

Abstract

Perovskite CsPbIBr2 is attracting ever‐increasing attention for carbon‐based, all‐inorganic solar cells, owing to its well‐balanced band gap and stability features. However, significant interfacial recombination of charge carriers in solar cells fabricated with this active layer, which is intrinsically associated with the unwanted conduction band misalignment between CsPbIBr2 and the commonly used TiO2 electron transport layer, has limited power conversion efficiency (PCE) values. Herein, we demonstrate successful conduction band alignment engineering at the TiO2/CsPbIBr2 heterojunction by modifying TiO2 with CsBr clusters. Such modification triggers a beneficial increase in the conduction band minimum (CBM) of TiO2 from −4.00 to −3.81 eV and decreases the work function from 4.11 to 3.86 eV, thus promoting favorable band alignment at the heterojunction, suppressing recombination, and improving extraction and transport of charge carriers. As a result, the carbon‐based, all‐inorganic CsPbIBr2 solar cells exhibit over 20 % enhancement in average PCE. The champion device achieves a PCE of 10.71 %, a record among pure CsPbIBr2‐based cells, open‐circuit voltage of 1.261 V, and excellent stability.

Inorganic CsPbIBr2‐Based Perovskite Solar Cells: Fabrication Technique Modification and Efficiency Improvement

“…c) UPS spectra of TiO 2 and TiO 2 /CsBr ETLs, and d) the corresponding energy band diagrams of the cell. Reproduced with permission . Copyright 2019, WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim.…”

“…In addition, after the study of a recent report by Zhu et al, they modified TiO 2 ETL by CsBr clusters to achieve a better conduction band alignment of TiO 2 /CsPbIBr 2 heterojunction . Attentively, the CsBr modifier had no apparent effect on the crystallinity and morphology of upper CsPbIBr 2 films.…”

“…e) Band alignment engineering of replacing TiO 2 by TiO 2 /CsBr. Reproduced with permission . Copyright 2019, WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim.…”

“…However, the device stability of CsPbI 2 Br‐based HPSCs is still a challenging task to overcome. Fortunately, CsPbIBr 2 achieves both goals of an acceptable bandgap of ≈2.05 eV for light absorption and a more superior phase stability, which can maintain stability up to its melting point more than 460 °C. As a welfare, for its particular bright‐red color, the CsPbIBr 2 material may also represent a promising candidate for applications in tandem devices and smart PV windows .…”

“…The crystal structure of the CsPbIBr 2 material was concisely introduced as a beginning, followed by the various fabrication procedures of perovskite films. Subsequently, some novel strategies were presented for film quality improvement, including fabrication methods’ improving, interface engineering, element impurity doping, etc . As a consequence, optoelectronic properties of the perovskite films by these methods are drastically improved.…”