Acid-free polyaniline:graphene-oxide hole transport layer in organic solar cells

Emeraldine-based polyaniline (EB-PANI) was synthesized via oxidative polymerization of aniline in aqueous acid. Various aliquots of graphene oxide (GO) aqueous dispersion were added to aniline during polymerization to achieve a mass percent of GO in the PANI:GO nanocomposites of 0%, 0.49%, 2.4%, 4.9%, 7.3%, 9.8%, 12.2%, and 24.5%, respectively. TEM images of the GO taken from different locations showed that most of the GO is either a double layer or multilayer graphene sheet—although some of the locations showed a single-layer graphene sheet. Raman shift of GO presents the G band located at 1591 cm⁻¹ and the D band located at 1321 cm⁻¹. The thermogravimetric analysis (TGA) of the PANI:GO nanocomposite showed the evidence of existing GO in PANI. The X-ray photoelectron spectroscopy (XPS) narrow scans of EB-PANI, GO, and PANI:GO showed a maximum that is assigned to the C–C peak position (284.8 eV). The deconvolution of the C1s peak in EB-PANI reveals the presence of C–N/C=N species (285.8 eV) assigned to the amine and imine nitrogens in polyaniline. The acid-free hole transport layer (HTL) synthesized from PANI:GO composites was used in two different types of organic solar cells (OPVs), i.e., P3HT:PC₆₀BM (1:0.6) and PCDTBT:PC₇₀BM (1:4). The highest power conversion efficiency (PCE) as a function of GO loadings in the PANI:GO nanocomposites for P3HT:PCBM cells was for the nanocomposite PANI:GO-7.5 with an average of ~ 0.2%, where the GO loading was 7.3% w/w. Equivalently, the PCDTBT:PCBM cells exhibited the highest PCE for PANI:GO-7.5 nanocomposite (~ 0.5%), as well.