Towards ab initio theory for organic photovoltaics
Xavier Blase
Institut Neel, CNRS and Universite Joseph Fourier, Grenoble, France

May 15, 2014, 1 p.m.


Initially developed in the mid-eighties at the ab initio level for inorganic semiconductors, a family of many-body perturbation theories, the so-called GW and Bethe-Salpeter (BSE) formalisms, have been shown recently to yield electronic and optical (excitonic) properties of bulk and gas phase organic systems with a remarkable accuracy. After introducing some of the important limitations associated with organic photovoltaic cells, we will show that key features, such as band gaps and offsets, bands dispersion, electron-phonon coupling strength, and donor-to-acceptor charge-transfer excitations, can be accurately described by such techniques that are parameter-free and allow the study of finite size or periodic systems comprising up to a few hundred atoms. Specific examples will be presented where the GW/BSE formalism outperforms existing density functional theory calculations with semilocal, global or range-separated hybrid functionals. Several challenges are however still ahead of such techniques, such as calculating excited states forces and phonons, or the development of specific discrete or continuous polarizable models. The selected calculations have been performed with a recently developed Gaussian-basis GW and BSE package, the Fiesta code.



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Towards ab initio theory for organic photovoltaics
Xavier Blase
Institut Neel, CNRS and Universite Joseph Fourier, Grenoble, France

May 15, 2014, 1 p.m.


Initially developed in the mid-eighties at the ab initio level for inorganic semiconductors, a family of many-body perturbation theories, the so-called GW and Bethe-Salpeter (BSE) formalisms, have been shown recently to yield electronic and optical (excitonic) properties of bulk and gas phase organic systems with a remarkable accuracy. After introducing some of the important limitations associated with organic photovoltaic cells, we will show that key features, such as band gaps and offsets, bands dispersion, electron-phonon coupling strength, and donor-to-acceptor charge-transfer excitations, can be accurately described by such techniques that are parameter-free and allow the study of finite size or periodic systems comprising up to a few hundred atoms. Specific examples will be presented where the GW/BSE formalism outperforms existing density functional theory calculations with semilocal, global or range-separated hybrid functionals. Several challenges are however still ahead of such techniques, such as calculating excited states forces and phonons, or the development of specific discrete or continuous polarizable models. The selected calculations have been performed with a recently developed Gaussian-basis GW and BSE package, the Fiesta code.



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