Sascha Sadewasser

Introduction of Si PERC Rear Contacting Designto Boost Efficiency of Cu(In,Ga)Se2 Solar Cells

Recently, Cu(In,Ga)Se2 (CIGS) solar cells have achieved 21% world-record efficiency, partly due to the introduction of a postdeposition potassium treatment to improve the front interface of CIGS absorber layers. However, as high-efficiency CIGS solar cells essentially require long diffusion lengths, the highly recombinative rear of these devices also deserves attention. In this paper, an Al2O3 rear surface passivation layer with nanosized local point contacts is studied to reduce recombination at the standard Mo/CIGS rear interface. First, passivation layers with well-controlled grids of nanosized point openings are established by use of electron beam lithography. Next, rear-passivated CIGS solar cells with 240-nm-thick absorber layers are fabricated as study devices. These cells show an increase in open-circuit voltage (+57 mV), short-circuit current (+3.8 mA/cm2), and fill factor [9.5% (abs.)], compared with corresponding unpassivated reference cells, mainly due to improvements in rear surface passivation and rear internal reflection. Finally, solar cell capacitance simulator (SCAPS) modeling is used to calculate the effect of reduced back contact recombination on high-efficiency solar cells with standard absorber layer thickness. The modeling shows that up to 50-mV increase in open-circuit voltage is anticipated.

Cd and Cu Interdiffusion in Cu(In, Ga)Se 2 /CdS Hetero-Interfaces

We report a detailed characterization of an industry-like prepared Cu(In, Ga)Se2 (CIGS)/CdS heterojunction by scanning transmission electron microscopy and photoluminescence (PL). Energy dispersive X-ray spectroscopy shows the presence of several regions in the CIGS layer that are Cu deprived and Cd enriched, suggesting the segregation of Cd–Se. Concurrently, the CdS layer shows Cd-deprived regions with the presence of Cu, suggesting a segregation of Cu–S. The two types of segregations are always found together, which, to the best of our knowledge, is observed for the first time. The results indicate that there is a diffusion process that replaces Cu with Cd in the CIGS layer and Cd with Cu in the CdS layer. Using a combinatorial approach, we identified that this effect is independent of focused-ion beam sample preparation and of the transmission electron microscopy grid. Furthermore, PL measurements before and after an HCl etch indicate a lower degree of defects in the postetch sample, compatible with the segregates removal. We hypothesize that Cu

Synthesis and formation mechanism of CuInSe2 nanowires by one-step self-catalysed evaporation growth

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Influence of CdS and Zn x Sn 1−x O y buffer layers on the photoluminescence of Cu(In, Ga)Se 2 thin films

Se nanodomains react during the chemical bath process to form these segregates since the chemical reaction that dominates this process is thermodynamically favorable. These results provide important additional information about the formation of the CIGS/CdS interface.

Growth of CuInSe 2 nanowires without external catalyst by molecular beam epitaxy

High-quality CuInSe2 (CISe) nanowires have been prepared by a one-step evaporation process. The presented growth process results in a composite material consisting of CISe NWs on top of a polycrystalline CISe base layer. The nanowires were extensively characterized by transmission electron microscopy, confirming their composition and atomic-scale crystal structure with a very low number of structural defects. From these analyses, we infer that the growth axis is along the [111] direction. The polycrystalline base layer has a tetragonal chalcopyrite structure and is optically active as confirmed by X-ray diffraction and photoluminescence (PL) analysis, respectively. Potential applications of this composite CISe NW/base-layer material for photovoltaic energy conversion are supported by the reduced reflectivity of the material and its strong PL intensity. The presented growth method is based on elemental evaporation under vacuum conditions, which makes the process compatible with the fabrication of photovoltaic devices.

Incorporation of alkali metals in chalcogenide solar cells

In this work, an optical study by photoluminescence on the influence of different buffer layers on a Cu(In,Ga)Se2 (CIGS) thin film is presented. Chemical bath deposited CdS was compared with atomic layer deposited ZnxSn1- xOy (ZnSnO). The CIGS bulk and CIGS/buffer interface in both samples are strongly influenced by fluctuating potentials, being less pronounced for the sample with the ZnSnO buffer layer. This study emphasizes the potential application of the ZnSnO semiconductor in CIGS based solar cells.The search for alternatives to the CdS buffer layer in Cu(In,Ga)Se<inline-formula><tex-math notation=LaTeX>

Rear surface optimization of CZTS solar cells by use of a passivation layer with nano-sized point openings

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CdS and Zn1−xSnxOy buffer layers for CIGS solar cells

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Passivation of Interfaces in Thin Film Solar Cells: Understanding the Effects of a Nanostructured Rear Point Contact Layer

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Optical and structural investigation of Cu2 ZnSnS4 based solar cells (Phys. Status Solidi B 11/2016)

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