Stability assessment of carbon-based hole-transport-layer-free perovskite solar cells under accelerated ageing: A combined experimental and predictive modelling analysis

Currently, the topic of stability of perovskite solar cells (PSCs) has seized the paramount attention of the scientific community in the direction of achieving technological maturing for real-world applications. The present paper demonstrates a comprehensive investigation of the stability of carbon-based hole-transport-layer-free (C-based HTL-free) PSCs under accelerated ageing, providing also a comparative insight into the dependence of the degradation of the devices performance due to their ageing on the type of the electron-transport-layer (ETL) employed (mesoporous or planar). A complete set of accelerated ageing experiments were considered, including prolonged isothermal ageing at a high or a freezing temperature, thermal shock cycling, damp heat ageing and bias stressing. A semi-analytical model ((residual property model (RPM)) developed previously by one of the authors was also applied to predict the degradation of the performance of the solar cells due to their ageing. The investigation demonstrates that there is no one-size-fits-all answer on which type of ETL results in higher stability in PSCs, with the estimated T70 lifetime of both types of encapsulated devices exceeding 1000 h for most of the ageing experiments. Among the studied environmental ageing conditions, humidity combined with high temperature was found to be the most rigorous extrinsic factor that can lead to the severe degradation of PSCs in the case of a sealant failure. On the other hand, of the internal factors, the abrupt thermal changes lead to the highest deterioration of the performance of these devices. Finally, RPM accurately predicted the experimental data for all cases of accelerated ageing tests, setting it as a powerful and universal tool for routine evaluation of PSCs lifetime and reliability for new and established applications.