Interplay of Photons and Charge Carriers in Thin-Film Devices

Abstract

Thin films are gaining ground in photonics and optoelectronics because of promising improvements in their efficiency and functionality, as well as decreased material usage compared with bulk technologies. However, the proliferation of thin films would benefit not only from continuous improvements in their fabrication, but also from a unified and accurate theoretical framework of the interplay of photons and charge carriers. In particular, such a framework would need to account quantitatively and self-consistently for photon recycling and interference effects. To this end, here, we combine the drift-diffusion formalism of charge-carrier dynamics and the fluctuational electrodynamics of photon transport self-consistently using the recently introduced interference-extended radiative-transfer equations. The resulting equation system can be solved numerically using standard simulation tools and, as an example, here, we apply it to study well-known GaAs thin-film solar cells. In addition to obtaining the expected device characteristics, we analyze the underlying complex photon-transport and recombination-generation processes, demonstrating the physical insight provided for unevenly excited structures through the direct and self-consistent description of photons and charge carriers. The methodology proposed here is general and can be used to obtain an accurate physical insight into a wide range of planar optoelectronic devices, of which the thin-film single-junction solar cells studied here are only one example.

Effects of resonances and surface texturing on light emission in emerging thin-film devices

“…( 5)] enters the structure in normal incidence similarly as in Ref. 14, with the ASTM G173 solar intensity considered for photon energies between 1.35 and 4.43 eV. To calculate R rad , photon energies between 1.35 and 1.65 eV are considered, and K values span from 0 to N GaAs k 0 .…”

“…On the other hand, we recently introduced an interference-extended radiative transfer model to solve FED self-consistently with the positiondependent quasi-Fermi levels from electrical transport modeling. 13,14 The results revealed peculiar net photon recycling processes taking place in thin-film solar cells, but we did not study how much resonances affected the total magnitude of the phenomenon.…”

“…For topic (2), we study how much resonances affect the EL of moderately thin layers (>100 nm) in a solar cell by carrying out two comparative electro-optical simulations with the same parameters: one based on conventional radiative transfer (RT) and another one based on fluctuational electrodynamics (through the interference-extended RT model deployed also in Ref. 14).…”

Resonance effects in the radiation transfer of thin-film intracavity devices

“…Studying the energy transport in thermophotonic cavity structures in this level of detail requires treatments where both emission and absorption within the cavity are fully accounted for. Here, we use a variant of fluctuational electrodynamics (FED) developed in our previous works [25][26][27]. Using this framework, we calculate emission-absorption rates attained in double-sided cavities, studying both total rates (incorporating all wavelengths and propagation angles) and the underlying optical mode structures.…”

“…Here, −ω corresponds to modes propagating in the negative direction, v = c/N (c speed of light in vacuum and N refractive index) is the speed of light in the medium, and ρ is the local density of states as defined in Ref. 26. The photon numbers in Eq.…”