Enhancement of All-Polymer Solar Cells by Addition of a Chlorinated Polymer and Formation of an Energy Cascade in a Nonhalogenated Solvent.

Abstract

Ternary organic solar cells (OSCs) containing a three-component photoactive layer with cascading energy alignments could benefit the charge transfer and improve the open-circuit voltage and power conversion efficiency. Herein, we report the incorporation of a derived chlorinated polymer, J52-Cl, as a guest donor into the donor J52 and acceptor N2200 blend film. The lowest unoccupied molecular orbital and the highest occupied molecular orbital levels of J52-Cl are between the corresponding energy levels of J52 and N2200, and this leads to generation of a cascade of energy levels. Photoluminescence measurements and the J-V of devices containing the donors indicated that this incorporation of J52-Cl could promote the charge transfer of the solar cells. The contribution from J52-Cl reduced the energy loss of J52-based binary devices significantly from 0.932 to 0.797 eV and the nonradiative energy loss from 0.399 to 0.269 eV, leading to an enhancement of Voc from 0.79 to 0.93 V. This introduction of chlorinated polymers also improves the intermolecular interactions and leads to a favorable morphology with appropriate phase separation and interpenetrating networks. As expected, the power conversion efficiency of ternary all-polymer solar cells (all-PSCs) processed in o-xylene solvent was increased from 8.55 to 11.02%. These results indicate that the ternary devices with the appropriate cascade of energy levels can fine tune the device's open-circuit voltage and finally improve the photovoltaic performance of OSCs.