Fundamental Flaw in the Current Construction of the TiO2 Electron Transport Layer of Perovskite Solar Cells and Its Elimination

Yan Yan; Cheng Liu; Yi Yang; Guoxiang Hu; Vandana Tiwari; De-En Jiang; Wei Peng; Ajay Jha; Hong-Guang Duan; Friedjof Tellkamp; Yong Ding; Weidong Shi; Shouqi Yuan; Dwayne Miller; Wanhong Ma; Jincai Zhao

doi:10.1021/acsami.1c09742

Fundamental Flaw in the Current Construction of the TiO₂ Electron Transport Layer of Perovskite Solar Cells and Its Elimination

ACS Appl Mater Interfaces. 2021 Aug 25;13(33):39371-39378. doi: 10.1021/acsami.1c09742. Epub 2021 Aug 15.

Authors

Yan Yan^{1

2

3}, Cheng Liu⁴, Yi Yang⁴, Guoxiang Hu⁵, Vandana Tiwari^{3

6}, De-En Jiang⁷, Wei Peng¹, Ajay Jha^{3

8

9}, Hong-Guang Duan^{3

10

11}, Friedjof Tellkamp³, Yong Ding⁴, Weidong Shi², Shouqi Yuan², Dwayne Miller^{3

11}, Wanhong Ma^{1

12}, Jincai Zhao^{1

12}

Affiliations

¹ Beijing National Laboratory for Molecular Sciences, Key Laboratory of Photochemistry, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, The Chinese Academy of Sciences, Beijing 100190, China.
² School of Chemistry and Chemical Engineering, Jiangsu University, No. 301, Xuefu Road, Zhenjiang 212013, China.
³ The Max Planck Institute for the Structure and Dynamics of Matter, Luruper Chaussee 149, Hamburg 22761, Germany.
⁴ State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Beijing 102206, China.
⁵ Department of Chemistry and Biochemistry, Queens College of the City University of New York, Queens, New York 11367, United States.
⁶ Department of Chemistry, University of Hamburg, Martin-Luther-King Platz 6, Hamburg 20146, Germany.
⁷ Department of Chemistry, University of California, Riverside, California 92521, United States.
⁸ The Rosalind Franklin Institute, Harwell Campus, Didcot, Oxfordshire OX11 0FA, U.K.
⁹ Research Complex at Harwell, Rutherford Appleton Laboratory, Didcot OX11 0QX, U.K.
¹⁰ Institut für Theoretische Physik, Universitat Hamburg, Jungiusstraße 9, Hamburg 20355, Germany.
¹¹ The Departments of Chemistry and Physics, University of Toronto, 80 Street George Street, Toronto M1C 1A4, Canada.
¹² University of Chinese Academy of Sciences, Beijing 100049, China.

PMID: 34433247
DOI: 10.1021/acsami.1c09742

Abstract

The top-performing perovskite solar cells (efficiency > 20%) generally rely on the use of a nanocrystal TiO₂ electron transport layer (ETL). However, the efficacies and stability of the current stereotypically prepared TiO₂ ETLs employing commercially available TiO₂ nanocrystal paste are far from their maximum values. As revealed herein, the long-hidden reason for this discrepancy is that acidic protons (∼0.11 wt %) always remain in TiO₂ ETLs after high-temperature sintering due to the decomposition of the organic proton solvent (mostly alcohol). These protons readily lead to the formation of Ti-H species upon light irradiation, which act to block the electron transfer at the perovskite/TiO₂ interface. Affront this challenge, we introduced a simple deprotonation protocol by adding a small amount of strong proton acceptors (sodium ethoxide or NaOH) into the common TiO₂ nanocrystal paste precursor and replicated the high-temperature sintering process, which wiped out nearly all protons in TiO₂ ETLs during the sintering process. The use of deprotonated TiO₂ ETLs not only promotes the PCE of both MAPbI₃-based and FA_0.85MA_0.15PbI_2.55Br_0.45-based devices over 20% but also significantly improves the long-term photostability of the target devices upon 1000 h of continuous operation.

Keywords: TiO2 electron transport layer; Ti−H species; deprotonation; perovskite solar cells.