Symmetry-Breaking Induced Dipole Enhancement for Efficient Spiro-Type Hole Transporting Materials: Easy Synthesis with High Stability

Spiral cores are crucial for designing efficient hole transporting materials (HTMs) for perovskite solar cells (PSCs), owing to their no-planar 3D architecture, high thermal stability, good solubility, and beneficial solid-state morphology. A lack of facile synthetic procedures for the spiral core limited the development of novel and stable spiral HTMs. In this regard, a one-step reaction is adopted to produce several novel acceptor-embedded spiral cores containing electron-withdrawing carbonyl group embedded orthogonal spiral conformation. After coupling with triphenylamine donors, symmetry-breaking spiral HTMs with uneven charge distribution can be obtained, bearing the advantages of adjustable dipole moment and enhanced structural stability. A combined theoretical and experimental study shows that the HTM with a stronger dipole moment can easily adsorb on the surface of perovskite via electrostatic potential, and the closer distance promoted facile hole transfer from perovskite to HTMs. In the end, PSCs based on strongly polarized spiro-BC-OMe achieved efficient hole extraction and thus an improved fill factor, promoting a power conversion efficiency (PCE) of 22.15%, and a module-based PCE of 18.61% with an active area of 16.38 cm(2). This study provides a new avenue for designing HTMs with strong dipole moments for efficient PSCs.

Automated summary

Spiral cores are crucial for efficient hole transporting materials in perovskite solar cells due to their 3D architecture, thermal stability, solubility, and solid-state morphology. This study introduces a one-step reaction to produce novel acceptor-embedded spiral cores with electron-withdrawing carbonyl groups, which can be coupled with triphenylamine donors to create symmetry-breaking spiral HTMs with adjustable dipole moments and enhanced stability. These HTMs can easily adsorb on the surface of perovskite and promote hole transfer, leading to improved efficiency in PSCs.