High-Performance Flexible Tandem Polymer Solar Cell Employing a Novel Cross-Linked Conductive Fullerene as an Electron Transport Layer

• Published in: Chemistry of materials Vol. 27; no. 5; pp. 1869 - 1875
• Main Authors: Chang, Chih-Yu, Huang, Wen-Kuan, Chang, Yu-Chia, Lee, Kuan-Ting, Siao, Hao-Yi
• Format: Journal Article
• Language: English
• Published: American Chemical Society 10.03.2015
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/acs.chemmater.5b00161

A novel thermally cross-linkable, n-doped conductive fullerene material is developed by incorporating tetrabutylammonium iodide (TBAI) as the dopant into an azidofullerene derivative PCBN3. The application of TBAI-doped cross-linked PCBN3 film as the electron transport layer (ETL) in polymer solar cells (PSCs) delivers several remarkable features, including easy solution-processability, reasonable electrical conductivity (2.8 × 10–3 S cm–1), good ambient and chemical stability, fine-tunability of the work function of the electrode, wide applicability in a variety of efficient polymers, relative weak thickness-dependent performance property, and moderate cross-linking temperature (∼140 °C). With this ETL, a single-junction solar cell based on the blend of poly­[[4,8-bis­[(2-ethylhexyl)­oxy]­benzo­[1,2-b:4,5-b′]­dithiophene-2,6-diyl]­[3-fluoro-2-[(2-ethylhexyl)­carbonyl]­thieno­[3,4-b]­thiophenediyl]] (PTB7) with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) delivers a power conversion efficiency (PCE) up to 8.8%, which is superior to that of the device with state-of-the-art ETL titanium oxide (TiO x ) film. In addition, the application of using this ETL in double-junction tandem structure solar cells is also demonstrated, with a PCE exceeding 10%. More significantly, the low processing temperature of this ETL makes it compatible with the fabrication of flexible tandem solar cells, and an impressively high PCE of 9.2% is demonstrated, which represents the highest PCE ever reported for flexible PSCs.