Reach-through band bending in semiconductor thin films

Roussillon, Y.; Giolando, Dean M.; Karpov, V. G.; Shvydka, Diana; Compaan, A.

doi:10.1063/1.1803950

Cited by 15 publications

(9 citation statements)

References 7 publications

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“…9 In superstrate solar cell design a buffer layer deposited on a conductive transparent electrode is often used to enhance the open circuit voltage and the fill factor, prevent the appearance of a potential barrier at the interface with conductive oxides 10 or induce charge redistribution in a solar cell via creation of defects in a CdS layer. 11 In the latter case, a solar cell comprising a conductive transparent electrode and a CdTe/CdS HJ can function as a metal-oxide-semiconductor (MOS) structure due to a significant density of acceptor traps in CdS. Therefore, using different buffer layers one can expect to alter electronic properties of CdS and change the electrostatic conditions at the CdTe/CdS heterojunction.…”

Section: Introductionmentioning

confidence: 99%

Modification of electron states in CdTe absorber due to a buffer layer in CdTe/CdS solar cells

Fedorenko

Major

Pressman

et al. 2015

Journal of Applied Physics

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By application of the ac admittance spectroscopy method, the defect state energy distributions were determined in CdTe incorporated in thin film solar cell structures concluded on ZnO, ZnSe, and ZnS buffer layers. Together with the Mott-Schottky analysis, the results revealed a strong modification of the defect density of states and the concentration of the uncompensated acceptors as influenced by the choice of the buffer layer. In the solar cells formed on ZnSe and ZnS, the Fermi level and the energy position of the dominant deep trap levels were observed to shift closer to the midgap of CdTe suggesting the mid-gap states may act as recombination centers and impact the open-circuit voltage and the fill factor of the solar cells. For the deeper states, the broadening parameter was observed to increase indicating fluctuations of the charge on a microscopic scale. Such changes can be attributed to the grain-boundary strain and the modification of the charge trapped at the grain-boundary interface states in polycrystalline CdTe.

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Section: Introductionmentioning

confidence: 99%

Modification of electron states in CdTe absorber due to a buffer layer in CdTe/CdS solar cells

Fedorenko

Major

Pressman

et al. 2015

Journal of Applied Physics

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“…The characteristics of the deep defect levels in the band gap of polycrystalline CdTe may be influenced by strain in the GBs, thus, suggesting high sensitivity of doping in CdTe to a particular deposition process and conditions of post-deposition anneals. CdTe is known as a "hard-to dope" semiconductor [8] implying that the concept of a metal-oxide-semiconductor (MOS) structure implemented either by restricting the dimensions of a metal electrode [9] or modifying charge trapping in the interfacing CdS [10] can lead to the electric field screening and enable modulation of the surface band bending in CdTe. In the latter case, intentional doping of CdS with copper, which diffuses along the grain boundaries from the back contact of CdTe, or incorporation of a resistive ZnO buffer layer next to CdS in the solar cell structure have been suggested to increase the effective screening length in ZnO/CdS layers and result in the higher values of the open circuit voltage (V OC ) in CdS/CdTe solar cells.…”

Section: Introductionmentioning

confidence: 99%

Electronic Properties of CdTe/CdS Solar Cells as Influenced by a Buffer Layer

et al. 2016

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We considered modification of the defect density of states in CdTe as influenced by a buffer layer in ZnO(ZnS, SnSe)/CdS/CdTe solar cells. Compared to the solar cells employing ZnO buffer layers, implementation of ZnSe and ZnS resulted in the lower net ionized acceptor concentration and the energy shift of the dominant deep trap levels to the midgap of CdTe. The results clearly indicated that the same defect was responsible for the inefficient doping and the formation of recombination centers in CdTe. This observation can be explained taking into account the effect of strain on the electronic properties of the grain boundary interface states in polycrystalline CdTe. In the conditions of strain, interaction of chlorine with the grain boundary point defects can be altered.

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“…It should also be noted that CdS is a rather thin low-resistivity low-compensated ntype semiconductor, so that the SCR is located practically only in the p-CdTe layer (see, e.g. [8,47]). So, for the CdS/ CdTe heterostructure, a schematic energy-band diagram of an abrupt asymmetric p-n junction or a Schottky diode can be applied (Fig.…”

Section: Recombination Losses and Requirements Imposed On Thickness Omentioning

confidence: 99%

“…The diffusion component of the quantum efficiency g dif is also found from the continuity equation. Taking into account recombination at the back surface of the CdTe layer and the boundary condition Dn = 0 at x = W, it can be written [44][45][46][47][48] where A = (d -W)/L n , D n and L n is the electron diffusion coefficient and diffusion length, S b is the velocity of recombination at the rear surface of the CdTe layer, and d is the thickness of the CdTe layer.…”

Section: Recombination Losses and Requirements Imposed On Thickness Omentioning

confidence: 99%

Possibilities to decrease the absorber thickness reducing optical and recombination losses in CdS/CdTe solar cells

Kosyachenko

2013

Mater Renew Sustain Energy

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Based on the optical constants, calculations of optical losses in CdS/CdTe solar cells have been carried out taking into account reflections at the interfaces and absorption in the TCO and CdS layers. It has been shown that the losses caused by reflections at the interfaces result in lowering the short-circuit current by *9 %, whereas absorption in the TCO and CdS layers with the typical thicknesses lead to losses of 15-24 %. Calculations of the integrated absorptive capacity of CdTe layer taking into account the spectral distributions of the standard AM1.5 solar radiation and the absorption coefficient of CdTe have been carried out. It is shown that in CdTe, the almost complete absorption of photons (C99.9 %) in the hv [ E g range is observed at a layer thickness of more than 20-30 lm, and the absorptive capacity of photons in a CdTe layer of thickness 1 lm is about 93 %. Based on the continuity equation and taking into account the recombination at the front and rear surfaces of the CdTe layer as well as in the space charge region, the restrictions imposed on the thickness of the absorber layer in CdS/CdTe heterojunction are studied. In all cases, along with the mobilities and lifetimes of charge carriers, the concentration of uncompensated impurities in CdTe plays a key role in the generation of photocurrent. When the CdTe absorber layer is thin (\1 lm), it is impossible to avoid a noticeable decrease of the short-circuit current density. The losses of the short-circuit current are equal to 19-20 % when the thickness of the CdTe layer is 0.5 lm whereas only 5 % for a typical thickness of 2-3 lm.

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Reach-through band bending in semiconductor thin films

Cited by 15 publications

References 7 publications

Modification of electron states in CdTe absorber due to a buffer layer in CdTe/CdS solar cells

Modification of electron states in CdTe absorber due to a buffer layer in CdTe/CdS solar cells

Electronic Properties of CdTe/CdS Solar Cells as Influenced by a Buffer Layer

Possibilities to decrease the absorber thickness reducing optical and recombination losses in CdS/CdTe solar cells

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