할로겐화 페로브스카이트 태양전지의 결정 성장 연구

Abstract

The perovskite material has attained considerable attention in various fields, including solar cells, light emitting diodes, and photoredox reaction. Among these fields, solar cells based on the halide perovskites have obtained great achievement and progress. The purpose of this dissertation is to study the grain growth during the conversion from precursor film to perovskite film and its application in solar cells. The fundamental mechanism of grain growth evolution in the fabrication process from the precursor phase to the perovskite phase is not fully understood despite its importance in achieving high quality grains in organic-inorganic hybrid perovskites, which is strongly affected by the processing parameters. In this work, we investigate the fundamental conversion mechanism from the precursor phase of perovskite to the complete perovskite phase, and how the intermediate phase promotes the growth of the perovskite grains during the fabrication process. By monitoring the morphological evolution of the perovskite during the film fabrication process, we observed a clear rod-shaped intermediate phase in the highly crystalline perovskite and investigated the role of the rod-like intermediate phase on the growth of the grains of the perovskite film. Furthermore, on the basis of these findings, we developed a simple and effective method to tailor grain properties including the crystallinity, size, and number of grain boundaries, and then utilized the film with the tailored grains to develop perovskite solar cells. To further study the underlying growth mechanism, the crystallization of MAPbI3 perovskite films was purposefully engineered to investigate the governing factors which determine their morphological properties and moisture stability. By modulating nucleation, we obtained a single layer perovskite film with controlled crystal facet orientation and grain size. The lack of perovskite nucleation sites during crystallization allowed us to tailor the resulting crystallization phase. Theoretical calculations indicated that the nucleation sites for perovskite growth are related to the electron density around the oxygen atom (C=O and S=O) in a Lewis base. A single layer of micrometer-sized and (110)-oriented perovskite crystals was achieved in the optimized MAPbI3 films via suppressing the formation of nucleation sites. We fabricated inverted perovskite solar cells with the structure of glass/ITO/PEDOT:PSS/ MAPbI3/PC61BM/Al which exhibited a high power conversion efficiency of 17.5% and a high fill factor over 83%. In addition, a study of the moisture stability indicated that the (110) facet orientation of the perovskite grains plays a more important role in film degradation than grain size. At last, a cost-effective fabrication method that can produce a remarkable enhancement in the device efficiency along with a reduction in the fabrication cost is one of the crucial requirements for the commercialization of perovskite-based solar cells. Here, we report a low-cost, printable, and highly effective synchronized-pressing annealing (SPA) method for inverted planar perovskite solar cells. In the SPA method, two films are combined face-to-face for annealing, and separated as in a roll-to-roll process. Consequently, the SPA method provides two homogeneous highly crystalline MAPbI3 films with monolithic millimeter-scale crystalline grains. The grains present a tendency of oriented growth along the <110> direction, parallel to the substrate, which leads to efficient charge transport. The inverted planar perovskite solar cells fabricated by the SPA method demonstrate high power conversion efficiencies of ~ 17% with significantly enhanced photocurrents and fill factors, when compared to conventionally fabricated devices. Moreover, the characteristics of both top and bottom devices are very similar, with nearly identical J–V curves and photoresponse spectra. As the SPA method is compatible with the printing technology for mass production, and as it can produce twin devices of high quality via one fabrication process, it can provide a remarkable reduction in the fabrication cost.