Stability improvement of MAPbI₃-based perovskite solar cells using a photoactive solid-solid phase change material

In this work, to increase the optical and thermal stability of perovskite solar cells, the composition of the perovskite layer is engineered by adding azobenzene (AZO) as a photoswitchable organic molecule. In this regard, solar cells with the FTO/b-TiO₂/m-TiO₂/CH₃NH₃PbI₃/HTM/Au structure are fabricated using spiro-OMETAD hole transporting layer. Remarkably, an improvement of the optical, thermal, and structural stability of the devices comprising 5%, 10%, and 20% AZO is observed. Through the solid-solid phase-change mechanism of AZO, harmful UV radiation is absorbed and leads to photoisomerization between the trans and cis isomers, thus aiding in the management of thermal stresses on the device. Devices with pure perovskite absorber layer and perovskite absorber layer containing 10 wt% AZO retained 43% and 70% of their initial performances, respectively, after 70 min of exposure to sunlight. Furthermore, after 1440 h of storage in ambient conditions (25 ℃ and 42% relative humidity), the reference device maintains 35% of its initial performance while the device containing 10 wt% AZO retains 89% of its initial performance. In the case of thermal stability, the device containing 10% AZO shows superior thermal stability by keeping about 55% of its initial efficiency after exposure to a temperature of 85 ℃ and one sun illumination, simultaneously, for 60 min, compared to the reference device which retains only 35% of its performance under the same condition.