Excellent intrinsic long-term thermal stability of co-evaporated MAPbI${}_3$ solar cells at 85 °C

Thermal stability is a critical criterion for assessing the long-term stability of perovskite solar cells (PSCs). Here, it is shown that un-encapsulated co-evaporated MAPbI${}_3$ (TE_MAPbI${}_3$) PSCs demonstrate remarkable thermal stability even in an n-i-p structure that employs Spiro-OMeTAD as hole transport material (HTM). TE_MAPbI${}_3$ PSCs maintain over ≈95% and ≈80% of their initial power conversion efficiency (PCE) after 1000 and 3600 h respectively under continuous thermal aging at 85 °C. TE_MAPbI${}_3$ PSCs demonstrate remarkable structural robustness, absence of pinholes, or significant variation in grain sizes, and intact interfaces with the HTM, upon prolonged thermal aging. Here, the main factors driving TE_MAPbI${}_3$ stability are assessed. It is demonstrated that the excellent TE_MAPbI${}_3$ thermal stability is related to the perovskite growth process leading to a compact and almost strain-stress-free film. On the other hand, un-encapsulated PSCs with the same architecture, but incorporating solution-processed MAPbI${}_3$ or Cs${}_{0.05}$(MA${}_{0.17}$FA${}_{0.83}$)${}_{0.95}$Pb(I${}_{0.83}$Br${}_{0.17}$)${}_3$ as active layers, show a complete PCE degradation after 500 h under the same thermal aging condition. These results highlight that the control of the perovskite growth process can substantially enhance the PSCs thermal stability, besides the chemical composition. The TE_MAPbI${}_3$ impressive long-term thermal stability features the potential for field-operating conditions. (© 2021 Wiley-VCH GmbH)