Realization of large open-circuit photovoltage in organic thin-film solar cells by controlling measurement environment

To obtain large open-circuit photovoltage (V-oc), we introduced a p-type semiconductor 5,6,11,12-tetraphenylnaphthacene (rubrene), which has a highest occupied molecular orbital (HOMO) level of 5.4 eV. Owing to an adsorption of O-2 and H2O into rubrene film, optical absorption peaks were markedly decreased after exposure in air. By controlling the measurement environment to prevent the adsorption of O-2 and H2O into rubrene films, we could obtain a high-performance organic thin-film solar cell with a large V-oc of 0.91 V.