title: CH3NH3PbI3films prepared by combining 1- and 2-step deposition: how crystal growth conditions affect properties.
abstract: Perovskite solar cells continue to attract strong attention because of their unprecedented rate of power conversion efficiency increase. CH3NH3PbI3(MAPbI3) is the most widely studied perovskite. Typically one-step (1-s) or two-step (2-s) deposition methods are used to prepare MAPbI3films. Here, we investigate a new MAPbI3film formation method that combines 1-s and 2-s deposition (termed 1 & 2-s) and uses systematic variation of the stoichiometric mole ratio (x) for the PbI2+ xMAI solutions employed. The PbI2+ xMAI solutions were used to deposit precursor films that were subsequently dipped in MAI solution as a second step to produce the final MAPbI3films. The morphologies of the 1 & 2-s MAPbI3films consisted of three crystal types: tree-like microcrystals (≫1 μm), cuboid meso-crystals (∼0.1-1 μm) and nanocrystals (∼50-80 nm). Each crystal type and their proportions were controlled by the value for x. The new 1 & 2-s deposition method produced MAPbI3films with tuneable optoelectronic properties that were related to those for the conventional 1-s and 2-s films. However, the 1 & 2-s film properties were not simply a combination of those for the 1-s and 2-s films. The 1 & 2-s films showed enhanced light scattering and the photoluminescence spectra displayed a morphologically-dependent red-shift. The unique morphologies for the 1 & 2-s films also strongly influenced PbI2conversion, power conversion efficiency, hysteresis and recombination. The trends for the performance parameters and hysteresis were compared for devices constructed using spiro-MeOTAD and P3HT and were similar. The 1 & 2-s method should apply to other perovskite formulations and the new insights concerning MAPbI3crystal growth conditions, morphology and material properties established in this study should also be transferable.
authors.affiliation: School of Materials, University of Manchester, MSS Tower, Manchester, M13 9PL, UK. brian.saunders@manchester.ac.uk.
authors.forename: Muhamad Z
authors.initials: MZ
authors.lastname: Mokhtar
authors.affiliation: School of Materials, University of Manchester, MSS Tower, Manchester, M13 9PL, UK. brian.saunders@manchester.ac.uk.
authors.forename: Mu
authors.initials: M
authors.lastname: Chen
authors.affiliation: Photon Science Institute, University of Manchester, Alan Turing Building, Oxford Road, Manchester, M13 9PL, UK.
authors.forename: Eric
authors.initials: E
authors.lastname: Whittaker
authors.affiliation: Photon Science Institute, University of Manchester, Alan Turing Building, Oxford Road, Manchester, M13 9PL, UK.
authors.forename: Bruce
authors.initials: B
authors.lastname: Hamilton
authors.affiliation: Department of Chemistry and Centre for Plastic Electronics, Imperial College London, South Kensington Campus, SW7 2AZ, UK.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Aristidou
authors.affiliation: School of Materials, University of Manchester, MSS Tower, Manchester, M13 9PL, UK. brian.saunders@manchester.ac.uk and School of Chemistry, University of Manchester, Manchester, M13 9PL, UK.
authors.forename: Simko
authors.initials: S
authors.lastname: Ramadan
authors.affiliation: School of Materials, University of Manchester, MSS Tower, Manchester, M13 9PL, UK. brian.saunders@manchester.ac.uk.
authors.forename: Ali
authors.initials: A
authors.lastname: Gholinia
authors.affiliation: Department of Chemistry and Centre for Plastic Electronics, Imperial College London, South Kensington Campus, SW7 2AZ, UK.
authors.forename: Saif A
authors.initials: SA
authors.lastname: Haque
authors.affiliation: School of Materials, University of Manchester, MSS Tower, Manchester, M13 9PL, UK. brian.saunders@manchester.ac.uk and School of Chemistry, University of Manchester, Manchester, M13 9PL, UK.
authors.forename: Paul
authors.identifier: http://orcid.org/0000-0001-8744-9174
authors.initials: P
authors.lastname: O'Brien
authors.affiliation: School of Materials, University of Manchester, MSS Tower, Manchester, M13 9PL, UK. brian.saunders@manchester.ac.uk.
authors.forename: Brian R
authors.identifier: http://orcid.org/0000-0003-1410-2967
authors.initials: BR
authors.lastname: Saunders