Terthieno[3,2-b]Thiophene (6T) Based Low Bandgap Fused-Ring Electron Acceptor for Highly Effcient Solar Cells with a High Short-Circuit Current Density and Low Open-Circuit Voltage Loss
Xueliang Shi1, Jingde Chen1,2, Ke Gao1, Lijian Zuo1, Zhaoyang Yao1, Feng Liu3,* Jianxin Tang2,* and Alex K.-Y. Jen1,4,*
1Department of Materials Science and Engineering University of Washington, Seattle, WA 98195-2120, USA.
2Institute of Functional Nano & Soft Materials (FUNSOM) Collaborative Innovation Center of Suzhou Nano Science and Technology Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Soochow University, Suzhou 215123, China
3Department of Physics and Astronomy, Shanghai Jiaotong University, Shanghai 200240, China.
4Department of Chemistry, City University of Hong Kong, Kowloon, Hong Kong, SAR, P. R. China.
A terthieno[3,2-b]thiophene (6T) based fused-ring low bandgap electron acceptor, 6TIC, is designed and synthesized for highly efficient nonfullerene solar cells. The chemical, optical, and physical properties, device characteristics, and film morphology of 6TIC are intensively studied. 6TIC shows a narrow bandgap with band edge reaching 905 nm due to the electron-rich π-conjugated 6T core and reduced resonance stabilization energy. The rigid, π-conjugated 6T also offers lower reorganization energy to facilitate very low VOC loss in the 6TIC system. The analysis of film morphology shows that PTB7-Th and 6TIC can form crystalline domains and a bicontinuous network. These domains are enlarged when thermal annealing is applied. Consequently, the device based on PTB7-Th:6TIC exhibits a high power conversion efficiency (PCE) of 11.07% with a high JSC > 20 mA cm-2 and a high VOC of 0.83 V with a relatively low VOC loss (≈0.55 V). Moreover, a semitransparent solar cell based on PTB7-Th:6TIC exhibits a relatively high PCE (7.62%). The device can have combined high PCE and high JSC is quite rare for organic solar cells.