The role of solvents in the formation of methylammonium lead triiodide perovskite

Metal halide perovskites(MHPs) are gaining increasing attention as low-cost, high-performance semiconductors for optoelectronics. In particular, their solution processing is compatible with the largescale manufacturing of thin-film devices, including solar cells and light-emitting diodes.Understanding the coordination chemistry in precursor-solvent solution and atomistic mechanisms of film formation is of great importance for optimizing the optoelectronic properties of the final films.Using the methylammonium lead triiodide(MAPbI_(3)) as an example, we study the complex evolution of the molecular species from the solution to the initial stage of the crystallization by using a combination of density functional theory(DFT) calculations and ab-initio molecular dynamics(AIMD) simulations. We focus on the widely employed solvents DMSO and DMF, analyze the structures and energies of the iodoplumbate complexes in the form of simple complex of [PbI_(m)L_(n)]^(2-m))_(x) and polymeric iodoplumbates of([PbI_(m)L_(n)]^(2-m))_(x). Based on the calculated formation enthalpies, we propose reaction schemes of MAPbI_(3) formation in DMSO, DMF and DMF-DMSO binary solvent and explain the advantages of the binary solvent.We highlight the important role of NH...O hydrogen bonds in the formation of iodoplumbates monomers.Our calculations indicate unbalanced reaction energies at several elementary reaction steps in either DMF(formation of [PbI_(4)L_(n)]^(2-) being highly favourable) or DMSO(formation of [PbI_(5)L_(n)]^(3- )being retarded).Mixing a small amount of DMSO in DMF gives rise to a better balance in the energies and, therefore,potentially better equilibria in the overall crystallization process and better quality of the final perovskite films.

CsPb(I_(x)Br_(1-x))_(3) solar cells

Owing to its nice performance, low cost, and simple solution-processing, organic-inorganic hybrid perovskite solar cell(PSC) becomes a promising candidate for next-generation high-efficiency solar cells.The power conversion efficiency(PCE) has boosted from 3.8% to 25.2% over the past ten years. Despite the rapid progress in PCE, the device stability is a key issue that impedes the commercialization of PSCs. Recently, all-inorganic cesium lead halide perovskites have attracted much attention due to their better stability compared with their organic-inorganic counterpart. In this progress report, we summarize the properties of CsPb(IxBr1-x)3 and their applications in solar cells. The current challenges and corresponding solutions are discussed. Finally, we share our perspectives on CsPb(IxBr1-x)3 solar cells and outline possible directions to further improve the device performance.