Читать книгу Perovskite Materials for Energy and Environmental Applications - Группа авторов - Страница 51

The power conversion efficiency of PSCs has risen due to considerable amount of research and focus on architectures, compositions, and manufacturing techniques. For commercialization of perovskite cell technology, it should be able to survive at minimum 25 years without degradation in yield in an external environment. In a controlled environment, high-efficiency solar cells are synthesized but when they are exposed to the ambient atmosphere, efficiency drops rapidly. Light absorbers are very fragile/sensitive to water, because of this, solar cells are unstable [38]. The degradation also depends on oxygen, UV radiation, and temperatures.

The rate of degradation of perovskite is very rapid (few minutes) when there is presence of water. The products formed after the degradation of perovskite are CH₃NH₃I and PbI₂. So to increase the lifetime of PSCs it should be kept away from moisture. An HTM with long alkyl chain was used, which would help to prevent water from passing from HTM to perovskite [48]. A carbon material layer of 10 μm thick was used as back contact to retain water. After these arrangements, the stability got increased and power conversion efficiency remained as it is for 1008 hours [49].

The formation of perovskite CH₃NH₃PbI₃ film is carried (annealing) at 100°C for 10 minutes [38]. During its annealiation process when the temperature crosses 120°C, the material(CH₃NH₃PbI₃) starts to degrade [50]. When temperature crosses 300°C, the perovskite splits into PbI₂, CH₃NH₂, and HI. Sometimes, TiO₂ can also bring instability because it can trap electrons in the crystals as it is nonstoichiometric, and this generally happens in an inert environment. So in seal-packed solar cells, there is a huge problem to avoid perovskite to get oxidized [38]. One solution is to dope TiO₂ with aluminium, which can greatly reduce the oxidation [51].

To some extent, the stability of the PSC has increased but it is still far away from long-term use and commercialization. For improving the stability the stability of PSCs, it is necessary to understand the degradation mechanisms and find out the state at which degradation reactions originated or accelerated [52].