Thiophene Oligomers with Low Cost and Easy Synthesis for Efficient Organic Solar Cells

Hole-transporting layer (HTL) materials with sufficient hole collection ability, noncorrosive nature, and easy preparation are strongly desired for the field of organic solar cells (OSCs). The development of new materials and synthetic methods has been proved to be the essential approach to improve the HTL performances. Herein, a series of thiophene oligomers TO-P1, TO-P2, and TO-P3 are designed and synthesized through coupling reaction by using the polyoxometalates as the oxidizing reagents. The thiophene oligomers can be readily synthesized under ambient condition with high yield. Among the as-prepared thiophene oligomers, TO-P2 exhibits neutral pH, sufficient work function, and high conductivity, endowing the HTL with excellent hole collection ability. Also, TO-P2 possesses good chemical stability and satisfied solution processability, which is important for practical use. By using TO-P2 as HTL, OSC shows a photovoltaic efficiency of 17.25%. Furthermore, TO-P2 is a universal HTL that can be used to fabricate efficient OSCs with various active layers. More importantly, TO-P2 shows good compatibility with large-area processing technique. A 1 cm² OSC is fabricated by using a blade-coated TO-P2 HTL, exhibiting a power conversion efficiency of 15.0%. The easy preparation and noncorrosive nature endow TO-P2 with great potential application in OSCs.