LiTFSI‐Free Spiro‐OMeTAD‐Based Perovskite Solar Cells with Power Conversion Efficiencies Exceeding 19

• Published in: Advanced energy materials 2019-08, Vol.9 (32), p.n/a
• Main Authors: Tan, Boer, Raga, Sonia R., Chesman, Anthony S. R., Fürer, Sebastian O., Zheng, Fei, McMeekin, David P., Jiang, Liangcong, Mao, Wenxin, Lin, Xiongfeng, Wen, Xiaoming, Lu, Jianfeng, Cheng, Yi‐Bing, Bach, Udo
• Format: Article
• Language: English
• Subjects: Apertures; Computer architecture; Energy conversion efficiency; Exposure; high performance; hole‐transporting material; LiTFSI‐free; Lithium; Morphology; Oxidation; perovskite solar cells; Perovskites; Photovoltaic cells; p‐doping; Reproducibility; Solar cells; Stability; Trifluoromethane
• ISSN: 1614-6832; 1614-6840
• DOI: 10.1002/aenm.201901519

To date, the most efficient perovskite solar cells (PSCs) employ an n–i–p device architecture that uses a 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenyl‐amine)‐9,9′‐spirobifluorene (spiro‐OMeTAD) hole‐transporting material (HTM), which achieves optimum conductivity with the addition of lithium bis(trifluoromethane)sulfonimide (LiTFSI) and air exposure. However, this additive along with its oxidation process leads to poor reproducibility and is detrimental to stability. Herein, a dicationic salt spiro‐OMeTAD(TFSI)2, is employed as an effective p‐dopant to achieve power conversion efficiencies of 19.3% and 18.3% (apertures of 0.16 and 1.00 cm2) with excellent reproducibility in the absence of LiTFSI and air exposure. As far as it is known, these are the highest‐performing n–i–p PSCs without LiTFSI or air exposure. Comprehensive analysis demonstrates that precise control of the proportion of [spiro‐OMeTAD]+ directly provides high conductivity in HTM films with low series resistance, fast hole extraction, and lower interfacial charge recombination. Moreover, the spiro‐OMeTAD(TFSI)2‐doped devices show improved stability, benefitting from well‐retained HTM morphology without forming aggregates or voids when tested under an ambient atmosphere. A facile approach is presented to fabricate highly efficient PSCs by replacing LiTFSI with spiro‐OMeTAD(TFSI)2. Furthermore, this study provides an insight into the relationship between device performance and the HTM doping level. Spiro‐OMeTAD(TFSI)2 is successfully employed in the fabrication of highly efficient n–i–p perovskite solar cells as a p‐dopant in the absence of lithium bis(trifluoromethane)sulfonimide (LiTFSI) and air exposure. With this approach, the proportion of [spiro‐OMeTAD]+ is precisely controlled, and the spiro‐OMeTAD(TFSI)2‐doped devices show a remarkably improved long‐term stability and well‐retained hole‐transporting material (HTM) morphology after aging for 300 h.