![]() ![]() Thorough studies on light-intensity dependence of short-circuit currents 21, 29, 30, 31, open-circuit voltages 21, 22, 31, 32, 33, 34, 35, and ideality factors of PSCs have been scarce 22, 36. Studies have evaluated various types of novel SCs in this regard, however, there is a gap in our knowledge of PSC operation. Because SRH is a first-order process, it can be distinguished from the second-order recombination process by examining light-intensity dependence of SC operation 22, 28. Trap-assisted carrier recombination, which is often called Shockley-Read-Hall (SRH) recombination, is a common mechanism that dominates loss of photo-generated carriers and eventually limits PCEs of various types of SCs 22, 27. For example, there were reports that J- V characteristics of hole-only methylammonium lead iodide (MAPbI 3) devices were consistent with traits of trap-assisted space-charge-limited current (SCLC) 24, 25, 26. Finally, judicious selection of precursors and anionic species was found to be efficient in alleviating hysteresis problems due to ionic species 5, 6, 9.ĭefects in PSCs can affect charge transport and recombination of photo-generated carriers. Similarly, interface engineering was applied to either passivate interface defects or establish proper energy barriers at the interface 5, 22, 23. Many previous studies, therefore, focused on enlarging grain size 5, 16, 18, 20 and passivating grain boundary 5, 16, 18. For example, grain size and/or grain boundary can affect the types and amounts of defects 16, 18, 19, 20. Some of these material issues are closely correlated to one another. Additionally, inorganic materials that are used in conjunction with halide perovskite layers for charge transport and extraction can result in extra interface defects 5, 22, 23. ![]() From a materials point of view, these issues arise from diverse morphological and compositional variations of halide perovskite materials 6, 16, 17, 18, 19, crystallization kinetics of halide perovskite grains 5, 16, 18, 19, 20, 21, various defects and/or remnant of precursors 16, 17, 18, 19, 20, and internal redistribution of ionic species within halide perovskite layers 6, 16, 17, 18, 19. ![]() Previous studies report various degrees of success in improving hysteresis, reproducibility, and stability 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, however, these issues remain to be fully resolved. Although PSCs can have power conversion efficiency (PCE) as high as 25.2% 4, they have inherent issues of large hysteresis, poor reproducibility, and limited stability. In recent years, a perovskite solar cells (PSCs) emerged as an intriguing new addition to the list of novel solar cells (SCs) that either challenge or complement already mature silicon SCs 1, 2, 3. The presence of multiple types of defects was corroborated by findings from equivalent-circuit analysis of impedance spectra. These ideality-factor values were consistent with those representing the intensity dependence of loss-current ratio estimated by using a constant internal-quantum-efficiency approximation. However, at high intensities, another type of defect not only took over monomolecular recombination, but also dominated bimolecular recombination to result in the ideality factor of ~2.0. At low intensities, monomolecular recombination occurred due to one of these defects in addition to bimolecular recombination to result in the ideality factor of ~1.7. Intensity dependence of ideality factor led us to the conclusion that there were two other types of defects that contributed mostly as recombination centers. Diode-like currents were analysed using a modified Shockley-equation model, the validity of which was confirmed by comparing measured and estimated open-circuit voltages. The variation of power-law exponent of SCLC showed that charge trapping by defects diminished as intensity increased, and that drift currents became eventually almost ohmic. ![]() Measured J- V curves consisted of space-charge-limited currents (SCLC) in a drift-dominant range and diode-like currents in a diffusion-dominant range. Its axis is perpendicular to the filter on the right (dark area)Īnd parallel to the filter on the left (lighter area).We investigated operation of a planar MAPbI 3 solar cell with respect to intensity variation ranging from 0.01 to 1 sun. This photograph, a polarizing filter is placed above two others. (c) When the secondįilter is perpendicular to the first, no light is passed. Is rotated, only part of the light is passed. The polarized light is passed by the second polarizing filter,īecause its axis is parallel to the first. Polarizing filters, where the first polarizes the light. ![]()
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