Organic-inorganic halide perovskite solar cells have emerged as a promising photovoltaic technology due to their superb power conversion efficiency (PCE) and very low material costs. While perovskite solar cells are expected to eventually compete with existing silicon-based solar cells on the market, their long-term stability has become a major bottleneck. In particular, perovskite films are found to be very sensitive to external factors such as air, UV light, light soaking, thermal stress and

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... thers. Among these stressors, light, oxygen and moisture-induced degradation can be slowed by integrating barrier or interface layers within the device architecture. However, the most representative perovskite absorber material, CH3NH3PbI3 (MAPbI3), appears to be thermally unstable even in an inert environment. This poses a substantial challenge for solar cell applications because device temperatures can be over 45 °C higher than ambient temperatures when operating under direct sunlight. In this thesis, the thermal stability of perovskite solar cells was primarily investigated. Initially, we systematically studied the effects of heating and cooling processes on the principal photovoltaic performance of perovskite solar cells by combining temperature-dependent J-V, steady-state PL, UV-VIS and time-resolved lifetime decay measurements. In particular, we have observed the dynamic evolution of degraded crystallinity, increased charge trapping, deep trap depth and PbI2 phase. During the heating process, the thermal degradation of the perovskite film was observed at 70 ° C or higher. An increase in the disordered phase of the perovskite film involved a drastic increase in charge trapping and the development of a deeper trap depth. Interestingly, we observed that the degradation of the perovskite film persisted even after the temperature was dropped, which led to irreversible J-V characteristics of the perovskite solar cell. Later, we introduced a polymer layer of PMMA which improved thermal stability for more than 1000hrs at 8 [...]