Selective photocurrent generation in the transparent wavelength range of a semiconductor photovoltaic device using a phonon-assisted optical near-field process

In this paper, we propose a novel photovoltaic device using P3HT and ZnO as test materials for the p-type and n-type semiconductors, respectively. To fabricate an electrode of this device, Ag was deposited on a P3HT film by RF-sputtering under light illumination (wavelength lambda (0)=660 nm) while reversely biasing the P3HT/ZnO pn-junction. As a result, a unique granular Ag film was formed, which originated from a phonon-assisted process induced by an optical near-field in a self-organized manner. The fabricated device generated a photocurrent even though the incident light wavelength was as long as 670 nm, which is longer than the long-wavelength cutoff lambda (c) (=570 nm) of the P3HT. The photocurrent was generated in a wavelength-selective manner, showing a maximum at the incident light wavelength of 620 nm, which was shorter than lambda (0) because of the Stark effect brought about by the reverse bias DC electric field applied during the Ag deposition.