13%-Efficiency Quaternary Polymer Solar Cell with Nonfullerene and Fullerene as Mixed Electron Acceptor Materials.

In this article, we report 13%-efficiency quaternary polymer solar cell. By introducing bis-PC71BM:PC71BM into a known nonfullerene system-poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl))benzo[1,2- b:4,5- b']dithiophene)- co-(1,3-di(5-thiophene-2-yl)-5,7-bis(2-ethylhexyl)benzo[1,2- c:4,5- c']dithiophene-4,8-dione):3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone-methyl))-5,5,11,11-tetrakis(4- n-hexylphenyl)-dithieno[2,3 d:2',3' d']- s-indaceno[1,2 b:5,6 b']dithiophene (PBDB-T:IT-M), the quaternary solar cell significantly outperforms the nonfullerene binary and the ternary (PBDB-T:IT-M:fullerene) devices with a significant increase in the short-circuit current-density (18.2 vs 16.5 and 16.8-17.5 mA/cm2) and the fill factor (0.73 vs 0.67 and 0.707-0.726), and hence, large power conversion efficiency (13% for quaternary vs 11% for the binary and 12% for the ternary). Grazing incidence wide-angle X-ray scattering data indicate that both the polymer and IT-M phase crystallinity becomes greater upon introduction of PC71BM as the forth additive into the host ternary PBDB-T:IT-M:bis-PC71BM, which results in an increase in both the electron and hole mobilities, contributing to the Jsc enhancement. Our results indicate that the use of the forth fullerene component provides more choices and more mechanisms than the ternary systems for tuning the photon-to-electron conversion; therefore, sheds light on the realization of high-efficiency polymer solar cells by designing the multiacceptor components with aligned energy levels, complementary absorption spectra, and improved film morphologies.