PHOTOVOLTAIC CHARACTERISTICS AND THEIR RELATIONSHIP WITH THE DEFECT STATES IN PEROVSKITE SOLAR CELLS

• Main Author: Asma Nurunnizar, Adhita
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/79520
• Institution: Institut Teknologi Bandung

The presence of defect states in perovskite solar cells affects their performance and stability. Defect states in perovskite solar cells arise due to the rapid perovskite crystallization and low-temperature process. In addition, perovskite crystals are dominated by ionic bonds which are quite weak compared to the covalent bonds in silicon solar cells, causing the possibility of various types of crystal defects such as vacancies, interstitial defects, lattice distortion by accumulated charges, and dissolved impurities. These various types of defects form deep and shallow traps that affect solar cell performance, so it is necessary to understand the mechanism and how far these defects affect solar cell performance. In this study, perovskite solar cells were made with a mesoscopic structure consisting of FTO/(TiO2 compact) c-TiO2/TiO2 mesopori (mpTiO2)/MAPbI3/PTAA/Emas (Au) layers. This research aims to observe the kinetics of transport and extraction of charge carriers by measuring transient photovoltage (TPV), to see the correlation between electronic processes, which can be affected by defect states caused by the characteristics of the mesoscopic structure of perovskite layers, and solar cell performance. In addition, a correlation study of solar cell performance and impedance characteristics obtained from Intensity Modulated Photovoltage Spectroscopy (IMVS) measurements was also carried out, which aims to understand the impact of charge carrier kinetics and ionic motion, due to surface or interface defects of the perovskite layer, on cell performance. Based on the research that has been done, the results show that the characteristics of the TPV curve show different characters for several fabricated cells. The observed TPV curve consists of a rise part and a decay part. The rise part is related to the cargo transport process, while the decay part is related to the recombination process in the perovskite layer with the transport layer. The elongated decay part indicates that there are more surface states in the perovskite/transport layer which causes trapping and detrapping of electrons. So the electrons take longer to reach the valence band of the perovskite layer. From this TPV measurement it is also found that the decay curve is a multiexponential decay consisting of fast decay, medium decay and slow decay. Fast decay with stretching exponential decay characteristics indicates the presence of non-simple first-order trapping and recombination processes that involve multitrapping processes including electron transport at the crystalline grain surface or interface. This fast decay is also related to the relaxation of structural surface defects, where this fast decay correlates with the appearance of semicircles in the low frequency region of the Nyquist plot of the IMVS measurement associated with ion migration or separation. In this study also used the passivation molecule TFA to reduce the effects of crystal defects that occur during manufacture, storage and when the cell is operating. The results show that cells with 5% TFA have the least trap density compared to other cells. In addition, measurements of cell efficiency on the fourth day after preparation showed that cells with TFA had better performance stability than cells without TFA. These results indicate that the TFA passivation molecule has the potential to be one of the candidate molecules that can be used to reduce the effects of the defective state in perovskite solar cells.