title: p-i-n heterojunctions with BiFeO3 perovskite nanoparticles and p- and n-type oxides: photovoltaic properties.
abstract: We formed p-i-n heterojunctions based on a thin film of BiFeO3 nanoparticles. The perovskite acting as an intrinsic semiconductor was sandwiched between a p-type and an n-type oxide semiconductor as hole- and electron-collecting layer, respectively, making the heterojunction act as an all-inorganic oxide p-i-n device. We have characterized the perovskite and carrier collecting materials, such as NiO and MoO3 nanoparticles as p-type materials and ZnO nanoparticles as the n-type material, with scanning tunneling spectroscopy; from the spectrum of the density of states, we could locate the band edges to infer the nature of the active semiconductor materials. The energy level diagram of p-i-n heterojunctions showed that type-II band alignment formed at the p-i and i-n interfaces, favoring carrier separation at both of them. We have compared the photovoltaic properties of the perovskite in p-i-n heterojunctions and also in p-i and i-n junctions. From current-voltage characteristics and impedance spectroscopy, we have observed that two depletion regions were formed at the p-i and i-n interfaces of a p-i-n heterojunction. The two depletion regions operative at p-i-n heterojunctions have yielded better photovoltaic properties as compared to devices having one depletion region in the p-i or the i-n junction. The results evidenced photovoltaic devices based on all-inorganic oxide, nontoxic, and perovskite materials.
authors.affiliation: Department of Solid State Physics, Indian Association for the Cultivation of Science , Jadavpur, Kolkata 700032, India.
authors.forename: Soumyo
authors.initials: S
authors.lastname: Chatterjee
authors.forename: Abhijit
authors.initials: A
authors.lastname: Bera
authors.forename: Amlan J
authors.initials: AJ
authors.lastname: Pal
keywords: BiFeO3 nanoparticles; MoO3 and ZnO nanoparticles; NiO; perovskites; photovoltaic properties of all oxide p−i−n heterojunctions; p−i−n heterojunctions