Sulfonated poly(diphenylamine) as a novel hole-collecting layer in polymer photovoltaic cells

Sulfonated poly(diphenylamine) (SPDPA) was used as a novel hole-collecting layer (HCL) in polymer photovoltaic (PV) cells. PV cells of poly(3-hexylthiophene) (P3HT):[ 6,6]-phenyl C-61 butyric acid methyl ester used as the active layer with SPDPA as HCL showed the higher power conversion efficiency (4.2%) and fill factor (0.68) than those with commercial poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (Baytron AI 4083) (3.6% and 0.65). The morphology change of the active layer was observed using atomic force microscopy and grazing-incidence X-ray diffraction. The hole-only device was fabricated to measure hole-injection current and hole mobility. The results show increased crystallinity of P3HT with SPDPA as HCL. The enhanced device performance is attributed to the improved hole mobility and the increased crystallinity of P3HT due to the properties of SPDPA.