Solution-processed nickel acetate as hole collection layer for polymer solar cells

We report efficient polymer solar cells (PSCs) based on poly(3-hexylthiophene) (P3HT) and indene-C-60 bisadduct (ICBA) with water soluble nickel acetate (NiAc) instead of acidic poly(ethylenedioxythiophene) : poly(styrene sulfonate) (PEDOT : PSS) as hole collection layer (HCL). The NiAc layer after thermal annealing at 150 degrees C for 30 min (alpha-NiAc) shows high transparency with light transmittance better than PEDOT: PSS in the wavelength range of 500-900 nm, high hole mobility of 1.3 x 10(-3) cm(2) V-1 s(-1) and suitable energy levels for application as HCL. The power conversion efficiency of the PSC based on P3HT/ICBA with the alpha-NiAc anode buffer layer reached 6.08% under the illumination of AM1.5G 100 mW cm(-2), which is among the best efficiencies of the P3HT-based PSCs. This work gives a new option for HCL selection in designing higher efficiency and more stable PSCs.