Organic photovoltaic cells with stable top metal electrodes modified with polyethylenimine.

ABSTRACT

Efficient organic photovoltaic cells (OPV) often contain highly reactive low-work-function calcium electron-collecting electrodes. In this work, efficient OPV are demonstrated in which calcium electrodes were avoided by depositing a thin layer of the amine-containing nonconjugated polymer, polyethylenimine (PEIE), between the photoactive organic semiconductor layer and stable metal electrodes such as aluminum, silver, or gold. Devices with structure ITO/poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) (PEDOTPSS)/poly(3-hexylthiophene)indene-C60-bis-adduct (P3HTICBA)/PEIE/Al demonstrated overall photovoltaic device performance comparable to devices containing calcium electron-collecting electrodes, ITO/PEDOTPSS/P3HTICBA/Ca/Al, with open-circuit voltage of 775±6 mV, short-circuit current density of 9.1±0.5 mA cm(-2), fill factor of 0.65±0.01, and power conversion efficiency of 4.6±0.3%, averaged over 5 devices at 1 sun.