Perovskite Solar Cells (PSCs) have achieved power conversion efficiencies exceeding 27% over the past decade. Despite rapid progress, chronic challenges related to stability and durability remain critical barriers to commercialization [1]. Incorporating mixed cations, specifically formamidinium (FA+) and methylammonium (MA+), has emerged as a promising strategy to enhance the perovskite stability and durability.
Preliminary studies demonstrated that FAPbI3 and MA0.5FA0.5PbI3 films prepared under ambient conditions (40-60% relative humidity), exhibit high crystallinity, uniform morphology, and predominant photoactive FAPbI3 ?-phase. These compositions retained 80% initial efficiency for 3160 hours demonstrating environmental resilience [2].
In this work, we investigate the electronic charge carrier dynamics of these mixed cations perovskites and elucidate how these dynamics affect the durability of PSCs [3]. To achieve these goals, we employed complementary techniques such as Transient Absorption Spectroscopy (TAS), Time-resolved photoluminescence (TRPL). These techniques provide insights into non-radiative and radiative recombination pathways, respectively. For samples with FTO?ETL?Perovskite architectures, TAS revealed that perovskites exhibit a bleach at the band-edge transition (760 nm), followed by its recovery through second-order kinetics. FA-rich perovskites exhibit a faster bleach recovery compared to MA-rich, observed by the linear dependence of ?A-1 vs. time, indicating efficient charge extraction to the ETL’s conduction band and reduced trap-mediated recombination due FA structural stability. In contrast, TRPL measurements quantified carrier lifetimes via biexponential decay fits, where the longest component directly correlates with structural stability. FA-rich perovskite, exceeding 1000 ns (for example for FAPbI3: 1085 ns), while MA-rich showed significantly shorter lifetimes, which are within the instrument detection limit in this sample. The reduced lifetime in MA-rich perovskites arises from lattice distortions and accelerated non-radiative recombination, where the free charger carriers are lower due to recombination processes.
These findings align with studies linking cation engineering to stability enhancements. To resolve charge transport and degradation mechanisms, we employ electrochemical impedance spectroscopy (EIS) to extract time constants in ?s-ms range, and model charge transport using equivalent circuits.
This work mapped the interplay between cation composition, recombination pathways, and device durability by correlating TAS, TRPL, and EIS data. FA-based perovskites demonstrate superior stability, whereas MA-rich devices require defect passivation to mitigate non-radiative losses.
The authors gratefully acknowledge Professor Dr. Prashant Kamat (University of Notre Dame) for his availability and experiments in transient absorption spectroscopy (TAS) and time-resolved photoluminescence (TRPL) measurements. We also would like to acknowledge the financial support of FAPESP (grant no. 2017/11986-5, 2022/07268-8) and Shell and the strategic importance of the support provided by ANP (Brazil National Oil, Natural Gas, and Biofuels Agency), CNPq (408672/2021-8; 406470/2022-7; 141608/2023-4; 306827/2023-9), and for the Multiuser Experimental Center of ABC (CEM – UFABC) for the experimental support.
References:
[1] M. Awais, Chem. Mater. 34, 18, 8112-8118 (2022).
[2] L. Polimante, Sol. Energy Mater. Sol. Cells 285, 113522 (2025).
[3] L. Polimante, Mater. Lett. 387, 138255 (2025).
Comissão Organizadora
Pedro Alves da Silva Autreto
Comissão Científica
Ferramenta completa de submissão, avaliação e publicação de anais para eventos científicos.
