Organic solar cells based on graphene derivatives and eutectic alloys vacuum-free deposited as top electrodes

Abstract

Here is presented the use of two graphene derivatives in organic solar cells (OSCs) based on PTB7:[70]PCBM active layer. Reduced graphene oxide (rGO) was used as hole transport layer (HTL). Also, solution-processable functionalized graphene (SPFG) was incorporated as a third component in the active layer. Furthermore, the top electrode was either Field’s metal (FM): Bi/In/Sn or BS: Bi/Sn, eutectic alloys that melt at 62 and 138 °C, respectively; they are vacuum-free deposited by drop coating under normal atmosphere conditions. For OSCs with rGO as HTL, thin films were prepared by reiterative spin-deposition and thermal reduction of GO after each deposition. The best results were achieved for 6-rGO with a PCE = 5.50%, similar to that reached in control devices, i.e., PEDOT:PSS as HTL. On the other hand, ternary active layers were prepared by blending SPFG, at different weight ratios: 0, 2, 4, and 6 wt. %, with PTB7:[70]PCBM. An increment in PCE (6.73%) for OSCs with 4 wt. % of SPFG was found, which is 22% larger than that of the reference devices. Finally, PCEs of 5.52% and 5.31% were reached in OSCs fabricated and tested under normal room conditions with FM and BS, respectively.