Two non-halogen additives significantly improve the efficiency of PTB7-Th:PC71BM-based polymer solar cells in non-halogen solvent

Additives play a crucial role in finely controlling morphology of the active layer in polymer solar cells (PSCs). At present, most of the additives used in the active layer are halogen-containing additives, such as 1,8-diiodooctane, 1-chloronaphthalene, which is detrimental to large-scale industrial production due to their toxicity. Herein, two low-cost, non-halogen additives, 1,2,3,4-tetrahydronaphthalene (THN) and 1,2,3,4-tetrahydronaphthalen-1-one (1-THNO), were introduced into the traditional PTB7-Th:PC71BM PSCs. The results showed that the THN- or 1-THNO-processed PTB7-Th:PC71BM blend films owned more efficient exciton dissociation, charge transport and collection as well as good morphological properties, resulting in high short-circuit current density and fill factor than the blend films without additive in chlorobenzene (CB) solution. Therefore, the CB + THN- and CB+1-THNO-processed PSCs reached power conversion efficiency (PCE) of 9.30% and 10.03%, respectively, which displayed a considerably higher PCE than without additive-processed (only 4.97%). Meanwhile, the PSCs were further fabricated with the non-halogen solvent o-xylene (o-XY) to avoid the possible environmental and health problems. As a result, the o-XY+1-THNO-processed PSC obtained an excellent PCE of 9.51% (vs. 2.17% for additive-free PSCs), which was a relatively high PCE for the PTB7-Th:PC71BM-based PSCs processed by non-halogen solvent. Additionally, the THN- or 1-THNO-processed devices owned good generality in other systems (e.g. PCE over 18% for 1-THNO-treated PM6:L8-BO-based PSCs) and excellent stability compared to the additive-free device. In sum, our work effectively improved the performance of the PSCs by using two non-halogen additives, providing the possibility of large-scale production in the future.