In Situ Surface Fluorination of TiO2 Nanocrystals Reinforces Interface Binding of Perovskite Layer for Highly Efficient Solar Cells with Dramatically Enhanced Ultraviolet-Light Stability

Wanpei Hu; Zhiling Wen; Xin Yu; Peisen Qian; Weitao Lian; Xingcheng Li; Yanbo Shang; Xiaojun Wu; Tao Chen; Yalin Lu; Mingtai Wang; Shangfeng Yang

doi:10.1002/advs.202004662

In Situ Surface Fluorination of TiO₂ Nanocrystals Reinforces Interface Binding of Perovskite Layer for Highly Efficient Solar Cells with Dramatically Enhanced Ultraviolet-Light Stability

Adv Sci (Weinh). 2021 Mar 13;8(10):2004662. doi: 10.1002/advs.202004662. eCollection 2021 May.

Authors

Wanpei Hu¹, Zhiling Wen¹, Xin Yu¹, Peisen Qian¹, Weitao Lian¹, Xingcheng Li¹, Yanbo Shang¹, Xiaojun Wu¹, Tao Chen¹, Yalin Lu¹, Mingtai Wang², Shangfeng Yang¹

Affiliations

¹ Hefei National Laboratory for Physical Sciences at Microscale CAS Key Laboratory of Materials for Energy Conversion Anhui Laboratory of Advanced Photon Science and Technology Department of Materials Science and Engineering University of Science and Technology of China Hefei 230026 China.
² Institute of Solid State Physics Hefei Institutes of Physical Science Chinese Academy of Sciences Hefei 230031 China.

Abstract

Low-temperature solution-processed TiO₂ nanocrystals (LT-TiO₂) have been extensively applied as electron transport layer (ETL) of perovskite solar cells (PSCs). However, the low electron mobility, high density of electronic trap states, and considerable photocatalytic activity of TiO₂ result in undesirable charge recombination at the ETL/perovskite interface and notorious instability of PSCs under ultraviolet (UV) light. Herein, LT-TiO₂ nanocrystals are in situ fluorinated via a simple nonhydrolytic method, affording formation of Ti─F bonds, and consequently increase electron mobility, decrease density of electronic trap states, and inhibit photocatalytic activity. Upon applying fluorinated TiO₂ nanocrystals (F-TiO₂) as ETL, regular-structure planar heterojunction PSC (PHJ-PSC) achieves a champion power conversion efficiency (PCE) of 22.68%, which is among the highest PCEs for PHJ-PSCs based on LT-TiO₂ ETLs. Flexible PHJ-PSC devices based on F-TiO₂ ETL exhibit the best PCE of 18.26%, which is the highest value for TiO₂-based flexible devices. The bonded F atoms on the surface of TiO₂ promote the formation of Pb─F bonds and hydrogen bonds between F^- and FA/MA organic cations, reinforcing interface binding of perovskite layer with TiO₂ ETL. This contributes to effective passivation of the surface trap states of perovskite film, resulting in enhancements of device efficiency and stability especially under UV light.

Keywords: electron transport layer; fluorination; interface binding; perovskite solar cells; titanium oxide.