LAUSR

Creating an orthogonal printable hole-transporting layer (HTL) without damaging the underlying layer is still a major challenge in fabricating large-area printed inverted polymer solar cells (PSCs). In this study, we prepared orthogonal-processable fluorine-functionalized reduced graphene oxide (FrGO) series with various sheet sizes such as large-sized FrGO (1.1 µm), medium-sized FrGO, (0.7 µm), and small-sized FrGO (0.3 µm) and systematically investigate the size effect of FrGOs on the hole transport properties of PSCs. The FrGOs exhibit highly stable dispersion without change over 90 days in 2-propanol solvent, indicating very high dispersion stability. Decreasing the sheet size of FrGOs enhanced hole-transporting properties, resulting in power conversion efficiencies (PCEs) of 9.27% for PTB7-Th:EH-IDTBR and 9.02% for PTB7-Th:PC71BM-based PSCs. Compared to devices with solution-processed PEDOT:PSS, 14% enhancement of PCEs was achieved. Interestingly, the PCEs of devices with the smallest FrGO sheet is higher than the PCE of 8.77% of a device with vacuum-deposited MoO3. The enhancement in the performance of PSCs is attributed to the enhanced charge collection efficiency, decreased leakage current, internal resistance, and minimized charge recombination. Finally, Small-sized FrGO HTLs were successfully coated on the photoactive layer using spray coating method, and they also exhibited PCEs of 9.22% for PTB7-Th:EH-IDTBR and 13.26% for PM6:Y6-based inverted PSCs.