Structure and optical bandgap relationship of π-conjugated systems

• Published in: PloS one Vol. 9; no. 1; p. e86370
• Main Authors: Botelho, André Leitão, Shin, Yongwoo, Liu, Jiakai, Lin, Xi
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 2014; Public Library of Science (PLoS)
• Subjects: Algorithms; Bridged Bicyclo Compounds, Heterocyclic - chemistry; Chemistry; Computer Simulation; Data points; Donor materials; Electric Power Supplies; Electrochemistry; Energy conversion efficiency; First principles; Heterojunctions; Hydrocarbons; Materials Science; Mathematical models; Mechanical engineering; Models, Chemical; Models, Molecular; Molecular Conformation; Molecular Structure; Open circuit voltage; Optimization; Organic Chemicals - chemistry; Photochemistry; Photovoltaic cells; Photovoltaics; Physics; Polycyclic Aromatic Hydrocarbons - chemistry; Polymers; Polymers - chemistry; Quantum Theory; Short circuits; Short-circuit current; Solar cells; Spectroscopy; Structure-Activity Relationship; Theory; Thiophenes - chemistry
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0086370

In bulk heterojunction photovoltaic systems both the open-circuit voltage as well as the short-circuit current, and hence the power conversion efficiency, are dependent on the optical bandgap of the electron-donor material. While first-principles methods are computationally intensive, simpler model Hamiltonian approaches typically suffer from one or more flaws: inability to optimize the geometries for their own input; absence of general, transferable parameters; and poor performance for non-planar systems. We introduce a set of new and revised parameters for the adapted Su-Schrieffer-Heeger (aSSH) Hamiltonian, which is capable of optimizing geometries, along with rules for applying them to any [Formula: see text]-conjugated system containing C, N, O, or S, including non-planar systems. The predicted optical bandgaps show excellent agreement to UV-vis spectroscopy data points from literature, with a coefficient of determination [Formula: see text], a mean error of -0.05 eV, and a mean absolute deviation of 0.16 eV. We use the model to gain insights from PEDOT, fused thiophene polymers, poly-isothianaphthene, copolymers, and pentacene as sources of design rules in the search for low bandgap materials. Using the model as an in-silico design tool, a copolymer of benzodithiophenes along with a small-molecule derivative of pentacene are proposed as optimal donor materials for organic photovoltaics.