• Boschetto, Gabriele
• Krompiec, Michal
• Dziedzic, Jacek
• Skylaris, Chris-Kriton
• Xue, Hong-Tao

Abstract

Statistical block copolymers, composed of donor (D) and acceptor (A) blocks, are a novel type of material for organic photovoltaics (OPVs) devices. In particular a new series of polymers based on PBTZT-stat-BDTT-8, recently developed by Merck, offers high solubility in different solvents, and a high power conversion efficiency (PCE) in different device architectures. Although it is known that the electronic properties of these materials may be significantly affected by attaching different functional groups on different blocks, it is not fully clear how important the influence of the polymer composition (i.e., the D/A block ratio) is, even if previous studies suggest that this might also have an effect. Therefore, the effect of the polymer composition in terms of HOMO, LUMO energies, and band gap was explored by studying a number of long chain oligomers with more than 1000 atoms each and with different D/A ratios. This study, that is novel both conceptually and methodologically, was made possible by using the linear-scaling reformulation of DFT implemented in the ONETEP code. Our results showed that changing the composition has a significant effect on the electronic structure of statistical copolymers, making this an alternative and suitable strategy to obtain materials with desired properties. Also, a systematic analysis of the effect of a range of different substituents placed in the D and A blocks of PBTZT-stat-BDTT-8 was performed in order to investigate how this class of materials responds to functionalization. We found that it is not possible to know a priori using chemical intuition what kind of influence different types of functional groups may have on these systems, and therefore, computational modeling is essential.

Topics

• impedance spectroscopy
• density functional theory
• copolymer
• block copolymer
• functionalization
• power conversion efficiency