Calixarenes enabling well-adjusted organic-inorganic interface for inverted organic solar cells with 18.25% efficiency and multifold improved photostability under max power point tracking

Compared with organic solar cells (OSCs) adopting conventional architecture, inverted OSCs have offered generally better stability, where ZnO is the most widely used electron transporting layer (ETL) material. For ZnO-based inverted OSCs, a well-tuned interface of organic (active layer)-inorganic (ZnO film) with matched surface energy (gamma(S)) is critical for both high performance and high stability. In this work, two typical calixarenes, C4A and BuC4A, were employed as the tuning agents to adjust this organic-inorganic interface for ZnO-based inverted OSCs. As a result, with PM6:L8-BO as the active layer, significantly promoted power conversion efficiencies (PCEs) from 17.14% (for ZnO) to 18.25% (for ZnO/C4A) and 17.80% (for ZnO/BuC4A) were achieved. Photodynamic studies indicate that the enhanced performance is due to the faster charge extraction process, the suppressed recombination and more ideal internal electric field in ZnO/calixarene-based devices. In addition, well-matched interface energy and more ordered molecular aggregation in active layer effectively improved photostability and thermal stability for ZnO/calixarene-based devices. These results indicate that calixarenes could act as effective modifying agents of ZnO to improve inverted OSCs' performance and stability simultaneously, and likely also stimulate calixarenes' and other macromolecules' broader studies in other organic electronic devices.

Automated summary

This study used calixarenes as tuning agents to adjust the organic-inorganic interface and improve the performance and stability of ZnO-based inverted OSCs. The results showed that calixarenes could enhance the power conversion efficiency, photostability, and thermal stability of inverted OSCs.