CsI Enhanced Buried Interface for Efficient and UV‐Robust Perovskite Solar Cells

Abstract

PCE has reached 25.5% in less than one decade since the first report of all-solid-state PSCs in 2012. [5][6][7] Although remarkable progress has been made in device efficiency, there is still a huge gap toward the theoretical Shockley-Queisser limit efficiency (30.5%). [8] Besides the PCE, the long-term stability of PSCs is of great significance for commercial applications, but it could be affected by the interfacial degradation induced by various stresses. [3,4] In a typical planar n-i-p PSC structure, the perovskite absorber is sandwiched between an electron transport layer (ETL) and hole transport layer (HTL). The interfaces between perovskite and carrier transport layers have been considered crucial for the further improvement of efficiency and stability of PSCs. [9,10] On the one hand, the interfacial defects and imperfect band alignments would result in substantial nonradiative recombination losses and thus compromised PCE. [11,12] On the other hand, the degradation of PSCs derived from both perovskite/HTL interfaces and ETL/perovskite interfaces severely threatens the stability of PSCs. [13][14][15][16] Plenty of research has concentrated on stabilizing perovskite/ HTL interfaces via post-fabrication treatment and HTL modification. [17] However, the concentration of defects accumulating at the buried interface is even higher than that at the top interface, [18] which makes the buried interface equally significant as the top interface. Unfortunately, little attention has been paid to it, which is partly because of the difficulties in fabricating and investigating the buried interface. [19] Moreover, the perovskite film near the ETL interface bears the strongest illumination stress under operational condition. Especially under UV exposure, the photovoltaic (PV) performance of PSCs could drop dramatically with the halogen oxidation and Pb reduction because of the vulnerability of perovskite to UV light. [20,21] This process is further accelerated by the desorption of UV-activated oxygen from ETLs, which also exposes deep-level interfacial defects and thus affecting the charge collection. [22][23][24] Although various strategies have been adopted to modify the ETLs to reduce defects, [25][26][27][28][29] there is little research effort on the interaction between the modified ETLs and perovskite films. Recently, Dong and co-workers reported a perovskite/ ETL interface enhancement strategy where formamidinium iodide incorporated SnO 2 reacts with PbI 2 -excess perovskiteThe buried interface between the perovskite and the electron transport layer (ETL) plays a vital role for the further improvement of power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). However, it is challenging to efficiently optimize this interface as it is buried in the bottom of the perovskite film. Herein, a buried interface strengthening strategy for constructing efficient and stable PSCs by using CsI-SnO 2 complex as an ETL is reported. The CsI modification facilitates the growth of the perovskite film and eff...

Buried Interface Modification in Perovskite Solar Cells: A Materials Perspective

“…[103] Similarly, buried CsI modification is employed to improve the resistance to UV illumination. [118] Recently, Wang et al regulated the SnO 2 ETL with RbF. The active Rb + cations escape into bulk perovskite beyond modifying RbF onto the SnO 2 surface, which results in a suppressed ion migration in the perovskites as well as a reduced carrier non-radiative recombination at the SnO 2 /perovskite interface.…”

Complexation Engineering of Electron Transport Layers for High‐Performance Perovskite Solar Cells

“…Compared with those of the unmodified sample, the complex-modified samples exhibit faster τ 1 and slower τ 2 values, indicating faster electron transfer and slower recombination. [51,52] In addition, to study the effects of carrier transport and recombination in the complex modified PSCs, electrical impedance spectroscopy (EIS) was conducted. Figure 5c S3, Supporting Information.…”

“…Compared with those of the unmodified sample, the complex‐modified samples exhibit faster τ 1 and slower τ 2 values, indicating faster electron transfer and slower recombination. [ 51,52 ]…”

Ultraviolet Photocatalytic Degradation of Perovskite Solar Cells: Progress, Challenges, and Strategies

“…The better UV stability can be attributed to CsBr located at the interface covering UV‐induced catalytic reaction activity sites of TiO 2 . Recently, the CsI–SnO 2 complex was used as an ETL for the stable PSCs by Xu et al [ 67 ] However, they emphasized that the incorporation of Cs + into the perovskite at the bottom interface enhances the resistance against UV illumination. As shown in Figure 6b, the PbI 2 peaks (28.2°) of the pristine perovskite belong to UV‐induced decomposition after 500 h of UV aging, while part of the perovskite film's color changes from black to yellow.…”

“…b) XRD patterns and the corresponding photos of pristine and UV‐aged perovskite films based on SnO 2 and CsI–SnO 2 , Reproduced with permission. [ 67 ] Copyright 2021, Wiley‐VCH GmbH. c) Schematic illustration of the formation of the MAPbI x Cl 3− x interlayer.…”