N-type cathode interlayer based on dicyanomethylenated quinacridone derivative for high-performance polymer solar cells

A new p-conjugated electrolyte bis(dicyanomethylene)-quinacridone with two octyl-pyridium (DCNQA-PyBr) has been synthesized and employed as a solution-processed cathode interlayer (CIL) for polymer solar cells (PSCs). The devices exhibited simultaneously increased open-circuit voltage (V-oc), short-circuit current (J(sc)) and fill factor (FF). Overall, the PSCs with PCDTBT (poly[N-9 ''-heptadecanyl-2,7-carbazole-alt- 5,5-(40,7'-di-2-thienyl-2',1',3'-benzothiadiazole)]) as a donor and PC71BM ([6,6]-phenyl C-71-butyric acid methyl ester) as an acceptor incorporating a 13 nm DCNQA-PyBr interlayer exhibit a power conversion efficiency (PCE) of 6.96%, which is 1.3 times of that of the Al-only device. Most importantly, compared to the reference p-conjugated electrolyte QA-PyBr, DCNQA-PyBr shows much improved electron transport ability and conductivity. As a result, the DCNQA-PyBr based devices only show a slight decrease in electron transport upon increasing the thickness of the CIL, thus allowing a high PCE with a wide CIL thickness range from 5 nm to 40 nm. Furthermore, introducing DCNQA-PyBr as a CIL into the devices based on P3HT: PC61BM (P3HT - poly(3-hexylthiophene), PC61BM - [6,6]-phenyl C-61-butyric acid methyl ester) and PTB7: PC71BM (PTB7 = polythieno[3,4-b]-thiophene-co-benzodithiophene) also leads to significantly enhanced device performance, showing high PCEs of 3.91% and 8.23%, respectively. These results confirm DCNQA-PyBr to be a promising CIL material for solution-processed large-area PSCs.