title: Improving the Performance of Formamidinium and Cesium Lead Triiodide Perovskite Solar Cells using Lead Thiocyanate Additives.
abstract: Formamidinium lead triiodide (FAPbI3) is considered as an alternative to methylammonium lead triiodide (MAPbI3) because of its lower band gap and better thermal stability. However, owing to the large size of FA cations, it is difficult to synthesize high-quality FAPbI3thin films without the formation of an undesirable yellow phase. Smaller sized cations, such as MA and Cs, have been successfully used to suppress the formation of the yellow phase. Whereas FA and MA lead triiodide perovskite solar cells (PVSCs) have achieved power conversion efficiencies (PCEs) higher than 20 %, the PCEs of formamidinium and cesium lead triiodide (FA1-xCsxPbI3) PVSCs have been only approximately 16.5 %. Herein, we report our examination of the main factors limiting the PCEs of (FA1-xCsxPbI3) PVSCs. We find that one of the main limiting factors could be the small grain sizes (≈120 nm), which leads to relatively short carrier lifetimes. We further find that adding a small amount of lead thiocyanate [Pb(SCN)2] to the precursors can enlarge the grain size of (FA1-xCsxPbI3) perovskite thin films and significantly increase carrier lifetimes. As a result, we are able to fabricate (FA1-xCsxPbI3) PVSCs with significantly improved open-circuit voltages and fill factors and, therefore, enhanced PCEs. With an optimal 0.5 mol % Pb(SCN)2additive, the average PCE is increased from 16.18±0.50 (13.45±0.78) % to 18.16±0.54 (16.86±0.63) % for planar FA0.8Cs0.2PbI3PVSCs if measured under reverse (forward) voltage scans. The champion cell registers a PCE of 19.57 (18.12) % if measured under a reverse (forward) voltage scan, which is comparable to that of the best-performing MA-containing planar FA-based lead halide PVSCs.
authors: Department of Physics and Astronomy, Wright Center for Photovoltaics Innovation and Commercialization, The University of Toledo, Toledo, OH, 43606, USA.
authors: Yue
authors: http://orcid.org/0000-0003-1566-6537
authors: Y
authors: Yu
authors: Department of Physics and Astronomy, Wright Center for Photovoltaics Innovation and Commercialization, The University of Toledo, Toledo, OH, 43606, USA.
authors: Changlei
authors: C
authors: Wang
authors: Department of Physics and Astronomy, Wright Center for Photovoltaics Innovation and Commercialization, The University of Toledo, Toledo, OH, 43606, USA.
authors: Corey R
authors: CR
authors: Grice
authors: Department of Physics and Astronomy, Wright Center for Photovoltaics Innovation and Commercialization, The University of Toledo, Toledo, OH, 43606, USA.
authors: Niraj
authors: N
authors: Shrestha
authors: School of Electronic Science and Engineering, Southeast University, Nanjing, 210096, PR China.
authors: Jing
authors: J
authors: Chen
authors: Department of Physics and Astronomy, Wright Center for Photovoltaics Innovation and Commercialization, The University of Toledo, Toledo, OH, 43606, USA.
authors: Dewei
authors: D
authors: Zhao
authors: Department of Physics and Astronomy, Wright Center for Photovoltaics Innovation and Commercialization, The University of Toledo, Toledo, OH, 43606, USA.
authors: Weiqiang
authors: W
authors: Liao
authors: Department of Physics and Astronomy, Wright Center for Photovoltaics Innovation and Commercialization, The University of Toledo, Toledo, OH, 43606, USA.
authors: Alexander J
authors: AJ
authors: Cimaroli
authors: Department of Physics and Astronomy, Wright Center for Photovoltaics Innovation and Commercialization, The University of Toledo, Toledo, OH, 43606, USA.
authors: Paul J
authors: PJ
authors: Roland
authors: Department of Physics and Astronomy, Wright Center for Photovoltaics Innovation and Commercialization, The University of Toledo, Toledo, OH, 43606, USA.
authors: Randy J
authors: RJ
authors: Ellingson
authors: Department of Physics and Astronomy, Wright Center for Photovoltaics Innovation and Commercialization, The University of Toledo, Toledo, OH, 43606, USA.
authors: Yanfa
authors: Y
authors: Yan
mesh_terms: D000578:Amidines / Q000737:chemistry; D017610:Calcium Compounds / Q000737:chemistry; D002586:Cesium / Q000737:chemistry; D011211:Electric Power Supplies / Q000639:trends*; D007854:Lead; D010087:Oxides / Q000737:chemistry; D012993:Solar Energy; D013861:Thiocyanates; D014025:Titanium / Q000737:chemistry
chemical_list: D000578:Amidines; D017610:Calcium Compounds; D010087:Oxides; D013861:Thiocyanates; C059910:perovskite; D002586:Cesium; D007854:Lead; C077922:formamidine; D014025:Titanium
keywords: cesium; energy conversion; perovskite; renewable resources; solar cells