A Coplanar π-Extended Quinoxaline Based Hole-Transporting Material Enabling over 21 % Efficiency for Dopant-Free Perovskite Solar Cells

Developing dopant-free hole transporting materials (HTMs) is of vital importance for addressing the notorious stability issue of perovskite solar cells (PSCs). However, efficient dopant-free HTMs are scarce. Herein, we improve the performance of dopant-free HTMs featuring with a quinoxaline core via rational pi-extension. Upon incorporating rotatable or chemically fixed thienyl substitutes on the pyrazine ring, the resulting molecular HTMs TQ3 and TQ4 show completely different molecular arrangement as well as charge transporting capabilities. Comparing with TQ3, the coplanar pi-extended quinoxaline based TQ4 endows enriched intermolecular interactions and stronger pi-pi stacking, thus achieving a higher hole mobility of 2.08x10(-4) cm(2) V-1 s(-1). It also shows matched energy levels and high thermal stability for application in PSCs. Planar n-i-p structured PSCs employing dopant-free TQ4 as HTM exhibits power conversion efficiency (PCE) over 21 % with excellent long-term stability.

Automated summary

Developing efficient dopant-free hole transporting materials is crucial for enhancing the stability of perovskite solar cells. By rational pi-extension, researchers have improved the performance of dopant-free HTMs with a quinoxaline core, resulting in enhanced charge transporting capabilities and higher hole mobility. These materials show great potential for application in PSCs with improved power conversion efficiency and long-term stability.