| 초록 |
Recently, organic-inorganic hybrid perovskites have become a very popular study in the field of photovoltaics. There are many different methods for synthesizing the perovskite active layer, such as one-step deposition, two-step deposition, and vapor-assisted deposition. In two-step method, a cuboid-shaped perovskite morphology is often formed when a low concentrated MAI solution (~8 mg/ml) is used, due to fewer nucleation sites, whereas a compact-shaped perovskite morphology is formed when a highly concentrated MAI solution (30~50 mg/ml) is used. In both cases, increasing of grain size is observed when annealing time is expanded. In this work, we studied how process conditions affect structural and electrical properties of the resulting perovskite films and their device performance. In the first study, we synthesize a compact flat film perovskite layer, using sequential spin-coating deposition, and proceed to prolong the annealing time from the standard 10 min to 5 hours to achieve optimized grain quality and photovoltaic performance (more than 5 hour, sample degradation occurs). To further understand the effect of annealing time and the grain enhancement mechanism, the samples were analyzed using Kelvin Probe Force Microscopy (KPFM) and conductive AFM (c-AFM). We have found that the surface potential distribution of MAPbI3 is changed by varying the annealing time of the perovskite absorber layer which appears to be directly correlated with device performance. In the second study, different grain morphology (cuboid vs. compact film), and device structure (regular vs. inverted) were prepared, and temperature-dependent IV characteristics and external quantum efficiency were compared, which reveals how carrier transport behavior is influenced by different grain and device structures. |
