Enhanced efficiency and stability of carbon based perovskite solar cells using terephthalic acid additive

We report an effective method to modulate the perovskite crystallization by incorporating terephthalic acid (TPA) additive into the perovskite precursor solutions. The addition of TPA additive simultaneously facilitate nucleation and modulate the kinetics of crystal growth from solutions, enabling preparation of smooth and compact perovskite morphology with improved crystallization, grain uniformity, loading of perovskite into the TiO₂ mesopores and coverage area. Before deposition of perovskite films, an ultrathin wide bandgap dielectric MgO nanolayer is incorporated onto porous TiO₂ to retard the carrier recombination at the interface in the devices. The mechanism of the interaction between TPA and Pb²⁺ on the film-forming process of perovskite crystal was also analyzed. Consequently, by optimizing the TPA concentration, we obtained highly efficient and stable low-temperature processed electron transport material (HTM)-free carbon based perovskite solar cells (PSCs). The performance of the PSCs is significantly improved with the mean efficiency increasing from 11.5% ± 0.67% for the control structure to 14.29% ± 0.37% for the TPA modified structure. Furthermore, the TPA modified perovskite films and devices present much better thermal, UV and ambient air stability than the pristine perovskite films and devices, and the corresponding PSCs with TPA modification show excellent stability with efficiency approaching 94% after being exposed to ambient air for 21 days without encapsulation.