On laboratory for energy harvesting materials and device at Ulsan National Institute of Science and Technology in South Korea (Republic), we are now having the highest photo-induced power conversion efficiency of lead hybrid perovskite single layer solar cell over 25.5% as the certified record on the best research-cell efficiency chart in National Renewable Energy (https://www.nrel.gov/pv/cell-efficiency.html) under the guidance of Distinguished Prof. Sang Il Seok. In addition, we are aiming to be accomplishing the long-term irradiation stable perovskite under 1 Sun global tilt condition for targeting commercially available materials in devices. We are truly concerned to enable this critical issue as greatly worst stability of hybrid perovskite materials in fact.   

    Since the reporting the sequential (Nature Vol. 499, pp. 316–319 (2013), Nature Nanotechnology Vol. 9, pp. 927–932(2014), Science  Vol. 348, Issue 6240, pp.1234-1237 (2015) and Science  Vol. 356, Issue 6345, pp. 1376-1379 (2017)) and one-step (Nature Materials Vol. 13, pp. 897–903(2014) and Nature Vol. 517, pp. 476–480(2015)) processes  for the formations of high performance hybrid perovskite single layer in solar cell applications, we have found large different of long-term radiation stability in comparison between two processing hybrid perovskite solar cells as a our report in Nature Energy, https://doi.org/10.1038/s41560-021-00802-z, (2021).  In both processes, the some questions were raised ; first, is it related with different formation processes for formation of hybrid perovskite layers ? second, is it influenced by the starting materials as the use of isopropyl alcohol or not ? or third, can it be affected by both factors as using isopropyl alcohol and sequential process ? In some previous reports, there is a positive effect for improving quality of hybrid perovskite layer using alcohol in anti-solvent (ChemSusChem, Vol. 11 Issue 14, pp. 2348-2357 (2018)). On this basis, we believe that alcohol induced in perovskite precursor can be also leading to improve somewhat quality of hybrid perovskite layer. It seems to be beginning at the preparation of perovskite precursor to annealing process for formation of these layers. 

    To find evidences for the chemical effect of isopropyl alcohol in hybrid perovskite, we have conducted the synchrotron based in-situ grazing incident X-ray wide angle diffraction on the sequential, one-step and isopropyl alcohol induced one-step processes. Resultingly, we have found rather similar crystal growth in comparison between sequential and isopropyl alcohol induced one-step processes such as the better crystal qualities than its ordinary one-step processed hybrid perovskite layer. An potential chemical composition as isopropylamine molecule in/on hybrid perovskites layer by sequential and isopropyl alcohol induced one-step processes has been revealed through synchrotron based X-ray photoemission spectroscopy, Fourier transform infra-red spectroscopy and proton Fourier transform nuclear magnetic resonance investigations. It seems to be occurring  some kind of side chemical reaction process as transamination between the induced methylammonium chloride and isopropyl alcohol under the conditions of the complexed chemical environment in hybrid perovskite precursor. It is still difficult to prove the precise side reaction process. 

    Under this discovery, if we tried to use already synthesized a chemical compound as isopropylammonium chloride for formation of hybrid perovskite layer by one-step process, it shows the greatly improving orientation of alpha phased formamidinium lead tri-iodide film with all performance of solar cell device as ~23 % (without surface treatment by phenethylammonium iodide) and 24% (with surface treatment by phenethylammonium iodide). In particular, the remarkably increasing long-term radiation stability of this material has indicated in the test of dynamic current-voltage scanning under 1 Sun condition for 2000 hours (without surface treatment by phenethylammonium iodide). If we consider the scan rate as a scan per around 84 min., this device has well sustaining under large electric stress. We believe that to has further modification of this material can be potentially offering long-term metastable hybrid perovskite material as over a year in the energy harvesting device applications.  

For more information, please refer to our recent publication in Nature Energy (https://doi.org/10.1038/s41560-021-00802-z)

Thanks to Prof. Tae Joo Shin, Dr. Min Gyu Kim and Dr. Ki-jeong Kim in Pohang Accelerator Laboratory