Quantum-kinetic theory of steady-state photocurrent generation in thin films: Coherent versus incoherent coupling

Abstract

The generation of photocurrents due to coupling of electrons to both classical and quantized electromagnetic fields in thin semiconductor films is described within the framework of the nonequilibrium Green's function formalism. For the coherent coupling to classical fields corresponding to single field operator averages, an effective two-time intraband self-energy is derived from a band decoupling procedure. The evaluation of coherent photogeneration is performed self-consistently with the propagation of the fields by using for the latter a transfer matrix formalism with an extinction coefficient derived from the electronic Green's functions. For the "incoherent" coupling to fluctuations of the quantized fields, which need to be considered for the inclusion of spontaneous emission, the first self-consistent Born self-energy is used, with full spatial resolution in the photon Green's functions. These are obtained from the numerical solution of Dyson and Keldysh equations including a nonlocal photon self-energy based on the same interband polarization function as used for the coherent case. A comparison of the spectral and integral photocurrent generation pattern reveals a close agreement between coherent and incoherent coupling for the case of an ultra-thin, selectively contacted absorber layer at short circuit conditions.

Selection Metric for Photovoltaic Materials Screening Based on Detailed-Balance Analysis

“…Therefore, the recombination currents and in consequence the external luminescence quantum efficiency depend on outcoupling and optical properties of the device whereas the internal quantum efficiency depends primarily on the properties of the material (electron-photon and electron-phonon coupling). Note that in case of geometric features on the size of the wavelength, interference effects can modify the spontaneous emission rate and thereby Q i (Purcell effect) [60,61].…”

Microscopic Perspective on Photovoltaic Reciprocity in Ultrathin Solar Cells

“…The tiny gradient in the QFL reflects the high charge carrier mobility and the absence of fast recombination processes, and leads to the equivalence Q PV ≡ a, as shown in Ref. 19, where the short circuit current under monochromatic illumination is compared to the photocurrent obtained from the absorptance. The spectral rate of photon emission normal to the left surface into modes coupling to normally incident light as provided by with the modal Poynting vector computed directly from the photon GF via (14) is therefore compared to the corresponding generalized Kirchhoff law…”

Photovoltaics at the mesoscale: insights from quantum-kinetic simulation

“…As soon as objects depend on off-diagonal GF elements, such as in the case of electron-photon interaction selfenergies and interband polarization functions, it is no longer safe to neglect non-locality, i.e., a larger number of off-diagonal elements of the GF need to be evaluated. While in the case of intraband scattering, e.g., with optical phonons, the underestimation of coupling strength due to a diagonal approximation can be mitigated by a simple rescaling of the self-energy, this is not possible in the case of interband scattering, as the spectral shape of the joint density of states is very sensitive to the non-locality range [42].…”

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