The current study provides an insight into the thermal stability of perovskite solar cells (PSCs) and the factors causing their degradation. To this end, a systematic stability study was carried out on n-i-p type perovskite solar cells involving mesoporous TiO2 layer. The samples were subjected to varying moisture and thermal conditions under light soaking while being exposed to long-term indoor (5000h) and outdoor (75h) harsh environmental conditions (i.e. 30%-80% RH and 40 degrees C-70 degrees C). To identify performance and morphological changes of PSCs after exposure to thermal stress, advanced characterization techniques including impedance spectroscopy, scanning electron microscopy and glow discharge optical emission spectrometry along with I-V characteristics were used. The un-encapsulated samples exposed to high thermal stress (40-70 degrees C) show degradation in their efficiency more than 40% within the 75h of thermal stress. In contrast, the samples that were kept at room temperature were found to be very stable over 5000h.