The effect of the functionalization of multiple carrier transporting interlayers on the performance and stability of bulk heterojunction organic solar cells

In this paper, we describe how the functionalization of carrier transporting interlayers affects the performance and stability of poly(3-hexylthiophene): poly(3-hexylthiophene): 3′H-cyclopropa [8,25] [5,6] fullerene-C60-D5h(6)-3′-butanoic acid 3′-phenyl methyl ester (P3HT:PCBM)-based organic solar cells. Composites of graphene oxide (GO) with zinc oxide (ZnO), (GO+ZnO) and with poly(3,4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT:PSS) (GO+PEDOT:PSS) were produced by grafting the ZnO and PEDOT:PSS onto GO sheets using a molecular level functionalization approach. This molecular level attachment was confirmed based on X-ray diffraction patterns, an X-ray photoelectron spectroscopic analysis, and Raman spectroscopy. The functionalization interlayer helped to attach the PEDOT:PSS and ZnO firmly to the GO layer, thereby forming an air-resistant layer and also supporting the backflow of free carrier transfer from the photoactive layer to their respective electrodes. Consequently, the device fabricated with the ZnO+GO composite as an electron transport layer and the GO+PEDOT:PSS composite as a hole transport layer demonstrated a significant improvement in PCE (4.88%), reproducibility, and environmental stability (40% after 432 h). Thus, we confirmed that these air-resistant and fast carriers transporting composite layers will probably contribute significantly to the widespread commercialization of low-cost and easily fabricated organic solar cells.