Simple Polythiophene Solar Cells Approaching 10% Efficiency via Carbon Chain Length Modulation of Poly(3-alkylthiophene)

Poly(3-alkylthiophene)s are the most extensively studied polymeric materials in organic and hybrid solar cells due to the unique advantages of extremely low cost in material synthesis. However, the inferior power conversion efficiencies (PCEs) are still the main obstacle in the commercial applications of poly(3-alkylthiophene)-based solar cells. In this contribution, the carbon chain length of poly(3-alkylthiophene) is modulated to reveal its impact on the molecular packing and charge transport behaviors in neat films and bulk heterojunction films with nonfullerene small-molecule acceptors for the first time. The odd-even effect can be clearly observed in poly(3-alkylthiophene):ZY-4Cl bulk heterojunction films, which has a great impact on the charge transport behavior and device performance. The poly(3-pentylthiophene) (P3PT) cell achieves a significantly high PCE of nearly 10% and a desirable fill factor of similar to 71%, which are the highest values of P3PT-based solar cells to date. The boosted efficiency is attributed to the altered van der Waals surfaces of alkyl segments through density functional theory calculation. This work reveals the odd-even effects of the carbon chain length modulation on the molecular packing and interaction of polythiophene:nonfullerene blends, which casts a new light on optimizing low-cost polythiophene solar cells and other promising electronics.