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Doping ZnO with Water/Alcohol-Soluble Small Molecules as Electron Transport Layers for Inverted Polymer Solar Cells

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journal contribution
posted on 03.10.2016, 00:00 by Chang Liu, Lin Zhang, Liangang Xiao, Xiaobin Peng, Yong Cao
By doping ZnO with porphyrin small molecules (FNEZnP-OE and FNEZnP-T) as cathode electron transport layers (ETLs), the inverted polymer solar cells (i-PSC) with PTB7:PC71BM (PTB7: polythieno­[3,4-b]-thiophene-co-benzodithiophene, PC71BM:[6, 6]-phenyl-C71-butyric acid methyl ester) as the active materials exhibit enhanced device performance. While the power conversion efficiency (PCE) of the PSCs with pure ZnO ETL is 7.52%, that of the devices with FNEZnP-T-doped ZnO ETL shows a slightly improved PCE of 8.09%, and that of the PSCs with FNEZnP-OE-doped ZnO ETL is further enhanced up to 9.24% with an over 20% improvement compared to that with pure ZnO ETL. The better performance is contributed by the better interfacial contact and reduced work function induced by 9,9-bis­(30-(N,N-dimethylamino)­propyl)-2,7-fluorenes and 3,4-bis­(2-(2-methoxy-ethoxy)-ethoxy)-phenyls in the porphyrin small molecules. More importantly, the PCE is still higher than 8% even when the thickness of FNEZnP-OE-doped ZnO ETL is up to 110 nm, which are important criteria for eventually making organic photovoltaic modules with roll-to-roll coat processing.