Tailoring nucleation and growth of organic-inorganic halide perovskite for high efficiency perovskite solar cells
Nobuya Sakai a, Zhiping Wang a, David P. McMeekin a, Henry J. Snaith a, Sandeep Pathak b, Victor M. Burlakov c
a University of Oxford, Clarendon Laboratory, Parks rd, Oxford, 0, United Kingdom
b Indian Institute of Technology Delhi, Hauz Khas, New Delhi, Delhi 110016
c University of Oxford, Clarendon Laboratory, Parks rd, Oxford, 0, United Kingdom
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of International Conference Asia-Pacific Hybrid and Organic Photovoltaics (AP-HOPV17)
Yokohama-shi, Japan, 2017 February 2nd - 4th
Organizers: Tsutomu Miyasaka and Iván Mora-Seró
Poster, Nobuya Sakai, 014
Publication date: 7th November 2016

Metal halide perovskite thin films can be crystallized via a broad range of solution based routes, however, the quality of the final films is strongly dependent upon small changes in solution composition or processing parameters. It would therefore be useful to better understand the interplay between starting solution and final perovskite films quality.With the intention to achieve both large grains of high crystalline quality, and uniform films with no pinholes, it appears sensible to revisit the formulation of the excess-organic mixed halide deposition route, specifically understanding the interplay of varying the metal-halide source upon nucleation and growth and final film quality. In this work, we present an investigation the thin-film growth from several starting perovskite solution and its influencing factors. We have adopted the different precursor compositions by “fractional substitution” of PbCl2 with PbI2 in the mix-halide precursor composition (3CH3NH3I: 1-xPbCl2: xPbI2) to unravel the deep crystallization mechanism. Here, we have discovered that by substituting only a 2 mol% of PbCl2 with the PbI2 in the mix-halide precursor composition (3H3NH3I:PbCl2) we transform the nucleation and growth process in thin film fabrication. The presence of the PbI2 results in uniformly distributed quadrilateral shaped crystallites of tens of microns in size, just after the casting of the precursor film, as opposed to “precursor crystals” which usually proceed crystallization 1 with this mixed-halide recipe.  These crystals grow and impinge to form pinhole free films with highly-crystalline domains. By incorporating these films into regular planar heterojunction perovskite solar cells fabricated in humidity controlled air (humidity: ~17%), we achieved 19.1% current-density voltage (JV) measurer power conversion efficiency and 17.2% stabilized power output (SPO). Importantly,  we reached over 20% JV power conversion efficiency with the CH(NH2)2-based composition in humidity controlled air using with the understanding of crystallization process into the organic-inorganic halide perovskite materials.

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