Enhancing photovoltaic performance: Exploring quinoxaline donors in conjunction with Y6 and BTP-4Br small molecule acceptors via DFT calculations

Abstract

Bulk heterojunction organic solar cells have helped increase power conversion efficiency and characterize and analyze possible factors influencing the improvement of solar-electrical energy conversion. Research in the last decades showed the link between the molecular electronic structure and the morphology of the photoactive layer with the photovoltaic process. Furthermore, both distinctive features are linked to halogenation in the acceptor and donor molecules that constitute the photoactive layer. It is worth mentioning that more attention has been paid to acceptor molecules compared to donors, particularly from the point of view of quantum mechanical calculations. Due to this, in the present work, a systematic study is carried out through density functional theory on the variation of halogenation in donors PBQ5 and PBQ6, which demonstrated outstanding efficiency when introduced into the photoactive layer of an organic solar cell complexed with the Y6 acceptor. Firstly, the correspondence of the electronic structure of both donors with higher efficiency of PBQ6, compared to PBQ5, stands out. An example is the lower position of the HOMO frontier molecular orbital of PBQ6, which predicts a higher open-circuit voltage, just as the experiment shows. Likewise, a smaller gap between the HOMO and LUMO orbitals in PBQ6 proposes an increase in the short-circuit current. The proposal of halogen exchange yields results of significant interest. Theoretical approximations of crucial parameters such as Voc, Jsc, and FF reveal promising avenues for enhancing power conversion efficiency through strategic adjustments in halogenation. In closing, despite the multitude of factors at play in the photoconversion of an organic solar cell—a complexity that poses challenges within the realm of computational theoretical studies—we consider that the uncovered findings can provide valuable insights into the determinants to be manipulated in terms of electronic structure, thereby paving the way for achieving heightened efficiency in photoconversion.