Influence of moiety sequence on the performance of small molecular photovoltaic materials

Abstract

The purpose of this work is to study the impact of moiety sequence in the chemical structure of small molecular photovoltaic materials on their basic properties and photovoltaic performance. For this aim, two isomeric compounds, namely BDT(ThBTTh)₂ and BDT(BTTh₂)₂, have been designed and synthesized by exchanging benzothiadiazole and thiophene positions with a structural variation. As compared with BDT(BTTh₂)₂, BDT(ThBTTh)₂ possesses a lower melting point, a blue-shifted absorption spectrum in solution, and slightly lower-lying highest occupied and lowest unoccupied molecular orbitals. More interestingly, the hole mobility of the BDT(ThBTTh)₂ neat film is 0.1 cm² V⁻¹ s⁻¹, which is three-orders of magnitude larger than that of BDT(BTTh₂)₂. Furthermore, these two compounds display significantly different photovoltaic performance, 4.53% for BDT(ThBTTh)₂versus 1.58% for BDT(BTTh₂)₂ in terms of their power conversion efficiency.