Origin of photovoltaic effect in (Bi, Pb)2Sr2Ca2Cu3O10+δ /Ag heterostructure

We report I-V characteristics and remarkable photovoltaic effect of (Bi, Pb)2Sr2Ca2Cu3O10+δ/Ag (Bi-2223/Ag) heterostructure in the temperature range between 50 K and 340 K induced by purple-laser irradiation, which is closely related to the superconductivity of Bi-2223 and the charge transfer between silver electrode and the superconductor. Obvious photo-induced voltage has been observed in the whole temperature range with two polarity reversals at a critical temperature (Tpr1) above room temperature and at the superconducting transition temperature (Tc). A maximum value of the photo-induced voltage appears at the onset of superconducting transition temperature (Tm). We confirm that there exists a built-in electrical field at the interface of Bi-2223/Ag heterostructure, similar to that found in YBCO/Ag systems, which provides the separation force for the photo-induced electron-hole pairs. The origin of the built-in electric field below Tc is a result of charge diffusion or redistribution between silver and the superconducting Bi-2223 associated with the Proximity effect and Andreev reflection. The direction of the field is always pointing from the superconductor to the metallic electrode. Between Tc and Tpr1, the interface field pointing from metal to superconductor arises from the diffusion of electrons in the metal and holes in the superconductor. The additional polarity reversal of photo-induced open circuit voltage (Voc) at Tpr1, which was not observed in YBCO/Ag system, implies a possible change of charge carrier type in Bi-2223. Our data provide a new dimension of information for depicting a more comprehensive picture of Bi-2223/Ag heterostructure and may lead to new applications of this high temperature superconductor in the field of photo-electronic sensing devices.