title: Enhanced Charge Carrier Transport and Device Performance Through Dual-Cesium Doping in Mixed-Cation Perovskite Solar Cells with Near Unity Free Carrier Ratios.
abstract: PbI2-enriched mixed perovskite film [FA0.81MA0.15Pb(I0.836Br0.15)3] has been widely studied due to its great potential in perovskite solar cell (PSC) applications. Herein, a FA0.81MA0.15Pb(I0.836Br0.15)3film has been fabricated with the temperature-dependent optical absorption spectra utilized to determine its exciton binding energy. A ∼13 meV exciton binding energy is estimated, and a near-unity fraction of free carriers out of the total photoexcitons has been obtained in the solar cell operating regime at equilibrium state. PSCs are fabricated with this mixed perovskite film, but a significant electron transport barrier at the TiO2-perovskite interface limited their performance. Cs2CO3and CsI are then utilized as functional enhancers with which to substantially balance the electron and hole transport and increase the carriers (both electrons and holes) mobilities in PSCs, resulting in much-improved solar-cell performance. The modified PSCs exhibit reproducible power conversion efficiency (PCE) values with little hysteresis effect in the J-V curves, achieving PCEs up to 19.5% for the Cs2CO3-modified PSC and 20.6% when subsequently further doped with CsI.
authors.affiliation: Department of Mechanical Engineering and Centre of Nanofibers and Nanotechnology (NUSCNN), National University of Singapore 117576, Singapore.|Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR) , No. 08-03, 2 Fusionopolis Way, Innovis 138634, Singapore.
authors.forename: Tao
authors.initials: T
authors.lastname: Ye
authors.affiliation: Department of Mechanical Engineering and Centre of Nanofibers and Nanotechnology (NUSCNN), National University of Singapore 117576, Singapore.|Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR) , No. 08-03, 2 Fusionopolis Way, Innovis 138634, Singapore.
authors.forename: Miloš
authors.initials: M
authors.lastname: Petrović
authors.affiliation: Department of Mechanical Engineering and Centre of Nanofibers and Nanotechnology (NUSCNN), National University of Singapore 117576, Singapore.
authors.forename: Shengjie
authors.initials: S
authors.lastname: Peng
authors.affiliation: Department of Mechanical Engineering and Centre of Nanofibers and Nanotechnology (NUSCNN), National University of Singapore 117576, Singapore.
authors.forename: Jeremy Lee Kong
authors.initials: JL
authors.lastname: Yoong
authors.affiliation: Department of Mechanical Engineering and Centre of Nanofibers and Nanotechnology (NUSCNN), National University of Singapore 117576, Singapore.|Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR) , No. 08-03, 2 Fusionopolis Way, Innovis 138634, Singapore.
authors.forename: Chellappan
authors.initials: C
authors.lastname: Vijila
authors.affiliation: Department of Mechanical Engineering and Centre of Nanofibers and Nanotechnology (NUSCNN), National University of Singapore 117576, Singapore.|Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR) , No. 08-03, 2 Fusionopolis Way, Innovis 138634, Singapore.
authors.forename: Seeram
authors.identifier: http://orcid.org/0000-0001-8479-8686
authors.initials: S
authors.lastname: Ramakrishna
keywords: CsI doping; carrier mobility; exciton binding energy; interface engineering; perovskite solar cells; small perturbation method