Easy-processing saccharin doped ZnO electron extraction layer in efficient polymer solar cells

The performance of polymer solar cells is known to be critically dependent on the characters of the charge extraction layers. In this work, an efficient electron extraction layer (EEL) is developed by doping saccharin into precursor of ZnO. It shows that the introduction of saccharin helps to passivate defects in ZnO EEL and polish the interfacial contact, which lead to efficient charge transport and collection processes, suppressed charge recombination loss, and increased light photon utilization. In poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2–6-diyl)]:[6,6]-phenyl C71-butyric acid methyl ester (PTB7-Th:PC71BM) based cells, over 10% enhancement of power conversion efficiency (PCE) is obtained compared to that of the reference cell with pristine ZnO as EEL. This work proves that the strategy of precursor additive has potential to prepare highly efficient EEL for polymer solar cells.