A photovoltaic device structure based on internal electron emission

Abstract

There has been an active search for cost-effective photovoltaic devices since the development of the first solar cells in the 1950s (refs 1–3). In conventional solid-state solar cells, electron–hole pairs are created by light absorption in a semiconductor, with charge separation and collection accomplished under the influence of electric fields within the semiconductor. Here we report a multilayer photovoltaic device structure in which photon absorption instead occurs in photoreceptors deposited on the surface of an ultrathin metal-semiconductor junction Schottky diode. Photoexcited electrons are transferred to the metal and travel ballistically to—and over—the Schottky barrier, so providing the photocurrent output. Low-energy (∼1 eV) electrons have surprisingly long ballistic path lengths in noble metals4,5, allowing a large fraction of the electrons to be collected.Unlike conventional cells, the semiconductor in this device serves only for majority charge transport and separation. Devices fabricated using a fluorescein photoreceptor on an Au/TiO2/Ti multilayer structure had typical open-circuit photovoltages of 600–800mVand shortcircuit photocurrents of 10-18 μAcm−2under 100mWcm−2visible band illumination: the internal quantum efficiency (electrons measured per photon absorbed) was 10 per cent. This alternative approach to photovoltaic energy conversion might provide the basis for durable low-cost solar cells using a variety of materials.