Excellent Intrinsic Long-Term Thermal Stability of Co-Evaporated MAPbI₃ 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 MAPbI₃ (TE_MAPbI₃) PSCs demonstrate remarkable thermal stability even in an n-i-p structure that employs Spiro-OMeTAD as hole transport material (HTM). TE_MAPbI₃ 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_MAPbI₃ 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_MAPbI₃ stability are assessed. It is demonstrated that the excellent TE_MAPbI₃ 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 MAPbI₃ or Cs_0.05(MA_0.17FA_0.83)_0.95Pb(I_0.83Br_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_MAPbI₃ impressive long-term thermal stability features the potential for field-operating conditions.