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

. 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.