Dopant-Free Hole-Transport Materials Based on Methoxytriphenylamine-Substituted Indacenodithienothiophene for Solution-Processed Perovskite Solar Cells

Solution-processed hole transporting materials (HTMs) that are dopant-free show promise for use in low-cost, high-performance perovskite solar cells (PSCs). The highest-efficiency PSCs use organic HTMs, many of which have low mobilities and therefore require doping, which lowers the device stability. Additionally, these materials are not easily scaled because they often require complicated synthesis. Two new HTMs (IDT–TPA and IDTT–TPA) were synthesized, which contained either an extended fused-ring indacenodithiophene (IDT) or indacenodithienothiophene (IDTT) core and strong electron-donating methoxytriphenylamine (TPA) groups as the end-capping units. The extended conjugation in the backbone of IDTT–TPA resulted in stronger π–π interactions (3.321 Å) and a higher hole mobility of 6.46×10⁻⁴ cm² V⁻¹ s⁻¹ when compared with that of IDT–TPA (9.53×10⁻⁵ cm² V⁻¹ s⁻¹). A dopant-free, planar PSC that contained IDTT–TPA was fabricated and exhibited a high power conversion efficiency (PCE) of 15.7 %. This cell exhibited a higher PCE and less hysteresis than devices that contained IDT–TPA.