Carrier dynamics in highly-excited TlInS2: Evidence of 2D electron-hole charge separation at parallel layers

We report a comprehensive study of the time-resolved photoluminescence (PL), carrier recombination, and carrier diffusion under diverse laser pulse excitations in TlInS2. The 2Dlayered crystals were grown by Bridgman method without or by a small Erbium presence in the melt. The investigation expose large differences in two crystal types, although, a linear nonradiative lifetime and carrier diffusivity attain close values at high excitation with no contribution of the Auger recombination and absence of the band gap narrowing effect. Moreover, at high pulse power, we detect imprinted transient grating fringes which are attributed to new crystal phase formed by 2D electron-hole charge separation on local layers. The versatile model of the spontaneously polarized 2D-crystal has been developed to explain observed features and ergodicity of charge dynamic processes. The model embraces the planar stacking faults (PSFs) as a distortion which edge is acting as sink of strong recombination. The reduced occurrence of the PSFs in the Erbium doped TlInS2 is the main attribute which determines enhancement of PL by a factor of 50, and improves carrier diffusion along 2D-layers. The simulation permits to evaluate the PSFs sizes of about 0.7 m. Presented results allow improving 2D-crystal growth technology for novel sensor devices with separated excess charges

Carrier dynamics in highly-excited TlInS2: Evidence of 2D electron-hole charge separation at parallel layers

We report a comprehensive study of the time-resolved photoluminescence (PL), carrier recombination, and carrier diffusion under diverse laser pulse excitations in TlInS2. The 2Dlayered crystals were grown by Bridgman method without or by a small Erbium presence in the melt. The investigation expose large differences in two crystal types, although, a linear nonradiative lifetime and carrier diffusivity attain close values at high excitation with no contribution of the Auger recombination and absence of the band gap narrowing effect. Moreover, at high pulse power, we detect imprinted transient grating fringes which are attributed to new crystal phase formed by 2D electron-hole charge separation on local layers. The versatile model of the spontaneously polarized 2D-crystal has been developed to explain observed features and ergodicity of charge dynamic processes. The model embraces the planar stacking faults (PSFs) as a distortion which edge is acting as sink of strong recombination. The reduced occurrence of the PSFs in the Erbium doped TlInS2 is the main attribute which determines enhancement of PL by a factor of 50, and improves carrier diffusion along 2D-layers. The simulation permits to evaluate the PSFs sizes of about 0.7 m. Presented results allow improving 2D-crystal growth technology for novel sensor devices with separated excess charges

Unified Electromagnetic-Electronic Design of Light Trapping Silicon Solar Cells

A three-dimensional unified electromagnetic-electronic model is developed in conjunction with a light trapping scheme in order to predict and maximize combined electron-photon harvesting in ultrathin crystalline silicon solar cells. The comparison between a bare and light trapping cell shows significant enhancement in photon absorption and electron collection. The model further demonstrates that in order to achieve high energy conversion efficiency, charge separation must be optimized through control of the doping profile and surface passivation. Despite having a larger number of surface defect states caused by the surface patterning in light trapping cells, we show that the higher charge carrier generation and collection in this design compensates the absorption and recombination losses and ultimately results in an increase in energy conversion efficiency. The fundamental physics behind this specific design approach is validated through its application to a 3 μm thick functional light trapping solar cell which shows 192% efficiency enhancement with respect to the bare cell of same thickness. Such a unified design approach will pave the path towards achieving the well-known Shockley-Queisser (SQ) limit for c-Si in thin-film (<30 μm) geometries