Copper(II) chloride doped graphene oxides as efficient hole transport layer for high-performance polymer solar cells

Abstract

Effective hole transport layers (HTLs) are still critical and desirable for the fabrication of high-performance, high-stability and cost-effective polymer solar cells (PSCs). In this work, we report that the graphene oxide (GO) simply modified with CuCl2-doping (GO:CuCl2) can be used as an effective HTL to produce high-performance PSC based on poly[(ethylhexyl-thiophenyl)-benzodithiophene-(ethylhexyl)-thienothiophene]:[6,6]-phenyl C71 butyric acid methyl ester (PTB7-Th: PC71BM). As a result, the average power conversion efficiency (PCE) reaches 7.68%, remarkably higher than that of the device using pristine GO as HTL (7.10%) and comparable to that of the device with conventional HTL of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) (7.69%). UPS measurements suggest that the work function of GO:CuCl2 is slightly increased relative to that of undoped GO. AFM characterizations also reveal a more continuous film morphology for the deposited GO:CuCl2 layer on indium tin oxide (ITO). Such improvements render an ohmic contact as well as a better interfacial contact between the electrode and active layer, yielding improved open-current voltage (Voc), fill factor (FF) and thus enhanced PCE.