Structure and optical bandgap relationship of π-conjugated systems.
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.
Department of Mechanical Engineering and Division of Materials Science and Engineering, Boston University, Boston, Massachussetts, United States of America.
André Leitão
AL
Botelho
Department of Mechanical Engineering and Division of Materials Science and Engineering, Boston University, Boston, Massachussetts, United States of America.
Yongwoo
Y
Shin
Department of Mechanical Engineering and Division of Materials Science and Engineering, Boston University, Boston, Massachussetts, United States of America.
Jiakai
J
Liu
Department of Mechanical Engineering and Division of Materials Science and Engineering, Boston University, Boston, Massachussetts, United States of America.
Xi
X
Lin
D000465:Algorithms; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000737:chemistry; D003198:Computer Simulation; D011211:Electric Power Supplies; D004563:Electrochemistry; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D015394:Molecular Structure; D009930:Organic Chemicals / Q000737:chemistry*; D010777:Photochemistry; D011084:Polycyclic Aromatic Hydrocarbons / Q000737:chemistry; D011108:Polymers / Q000737:chemistry*; D011789:Quantum Theory; D013329:Structure-Activity Relationship; D013876:Thiophenes / Q000737:chemistry
D019086:Bridged Bicyclo Compounds, Heterocyclic; D009930:Organic Chemicals; D011084:Polycyclic Aromatic Hydrocarbons; D011108:Polymers; D013876:Thiophenes; C121383:poly(3,4-ethylene dioxythiophene)