Effect of atmospheres on the open-circuit photovoltage of nanoporous TiO2/poly(3-hexylthiophene) heterojunction solar cell

Photovoltaic properties of the nanoporous titanium dioxide TiO2/poly(3-hexylthiophene) heterojunction solar cell are studied by photovoltammetry under periodic photoirradiation, which is effective in examining the photo- and dark-current potential profiles simultaneously in the same experiment. The open-circuit voltage (Voc) of the TiO2/poly(3-hexylthiophene) cell significantly depends on the atmosphere in the measurements. Accompanying the increase of the dark current, the photovoltammogram in vacuo shows the lower Voc than that in air. The stepwise increase of the dark current after pulse irradiation is observed in the transient current-time profiles for the TiO2/poly(3-hexylthiophene) cell in vacuo. The difference spectra of the TiO2/poly(3-hexylthiophene) cell during photoirradiation in vacuo show the increase of a broad absorption band attributed to trapped charge carriers in the near-IR region, which is the origin of the dark current increment. The photovoltaic properties of the TiO2/poly(3-hexylthiophene) heterojunction are seriously affected by the trapped charge carriers.