Dopant-Free Donor (D)–π–D–π–D Conjugated Hole-Transport Materials for Efficient and Stable Perovskite Solar Cells

Fei Zhang^1,2,3,†, Xicheng Liu^4,†, Chenyi Yi², Dongqin Bi², Jingshan Luo², Shirong Wang^1,3,*, Xianggao Li^1,3,*, in Xiao^1,3, Shaik Mohammed Zakeeruddin^2,* and Michael Grätzel^2,*

^† These authors contributed equally.
¹ School of Chemical Engineering and Technology, Tianjin University, Tianjin, China
² Laboratory of Photonics and Interfaces, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
³ Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin, China
⁴ School of Chemistry and Chemical Engineering, Qufu Normal University, Qufu, China

DOI:  10.1002/cssc.201600905
First published online 25 Aug 2016
Paper on publisher's website
Paper in open access repository

Three novel hole-transporting materials (HTMs) using the 4-methoxytriphenylamine (MeOTPA) core were designed and synthesized. The energy levels of the HTMs were tuned to match the perovskite energy levels by introducing symmetrical electron-donating groups linked with olefinic bonds as the π bridge. The methylammonium lead triiodide (MAPbI₃) perovskite solar cells based on the new HTM Z34 (see main text for structure) exhibited a remarkable overall power conversion efficiency (PCE) of 16.1 % without any dopants or additives, which is comparable to 16.7 % obtained by a p-doped 2,2′,7,7′-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9′-spirobifluorene (spiro-OMeTAD)-based device fabricated under the same conditions. Importantly, the devices based on the three new HTMs show relatively improved stability compared to devices based on spiro-OMeTAD when aged under ambient air containing 30 % relative humidity in the dark.