Addressing the Function of Easily Synthesized Hole Transporters in Direct and Inverted Perovskite Solar Cells

Two simple small molecules are designed and successfully implemented here as hole-transporting material (HTM) in perovskite-based solar cells (PSCs). With the aim of elucidating the interconnection between molecular structure, properties, and their role in the working devices, these HTMs are implemented in both thin planar direct (n-i-p) and inverse (p-i-n) geometries. It is observed how the HTM layer morphology influences the photovoltaic performance. Moreover, from analysis of the different devices, fundamental information is retrieved on the factors influencing small molecule hole extracting/transporting functionality in PSCs. Specifically, two main roles are identified: When HTMs are introduced as growing substrate (p-i-n), there is a positive impact on the device performance via influence of perovskite formation; meanwhile, their efficacy in transporting the holes governs the performance of direct configurations (n-i-p). These findings can be extended to a wide family of small molecule HTMs, providing general rules for refining the design of novel and more efficient ones.