Manfred Ruske

Transparent and conductive ZnO:Al films deposited by large area reactive magnetron sputtering

A new coating technology has been developed for large area deposition of transparent and conductive ZnO:Al films. Reactive AC magnetron sputtering from metallic Zn:Al has been performed at low substrate temperature below 200 °C using the new CleanMag technology of applied films based on moving magnets for layers with low defect density and with conventional reactive AC magnetron sputtering using static magnets (Applied Films TwinMag). Process stabilization at non-stable process conditions in transition mode has been achieved using closed loop control of discharge power according to fast oxygen partial pressure measurements taken by a lambda probe. Films with film thickness of 800–1000 nm deposited with dynamic deposition rate of aD>60 nm m/min exhibit low resistivity of ρ<270 μΩ cm and small absorption (k<2×10−3) in the visible range. The homogeneity of sheet resistance on float glass substrates with dimension of 600×1000 mm2 is better than ±6%. Film properties such as etching characteristics and haze can be controlled due to adjustment of total pressure and substrate temperature for large are a-Si:H thin film photovoltaic applications [1].

State-of-the-art mid-frequency sputtered ZnO films for thin film silicon solar cells and modules

This article reports on the use of ZnO films in silicon thin film p-i-n solar cells and modules. It summarizes the status in the final phase of a joint research project aiming at the development of high-quality ZnO/glass substrates feasible for an industrial solar module production. The samples were prepared by reactive mid-frequency (mf) sputtering on large area (60×100 cm 2 ) glass sheets using low-cost metallic Zn:Al targets. These ZnO films exhibit resistivities down to 2.6×10 -4 Ω cm and high optical transmittance. Variation of the sputter pressure leads to films with significantly differing etching behavior in diluted acids. ZnO layers prepared in the high pressure regime develop strongly textured light scattering surfaces after etching, which is necessary to obtain highly efficient solar cells. Initial efficiencies of small area amorphous silicon (a-Si:H) cells on texture-etched ZnO-films prepared by mf-sputtering on 60×100 cm 2 soda-lime glass (3 mm thick) range from 8 to 9% (highest efficiency 9.2%, i-layer thickness 350 nm). First 0.6 m 2 modules on ZnO prove the principal applicability of the films for an industrial manufacturing process.

Upscaling of texture-etched zinc oxide substrates for silicon thin film solar cells

Abstract Large area (320×400 mm2) glass/ZnO-films were prepared by high-rate d.c. magnetron sputtering from ceramic targets and compared to lab-type r.f.- and m.f.-sputtered ZnO. The very uniform and initially smooth films exhibit excellent electrical and optical properties (resistivity ≤5×10−4 Ωcm, transmission >80% for visible light and 1500-nm thick films). Upon etching in diluted hydrochloric acid they develop a surface texture. Independent of sputter technique (d.c. or r.f.) and substrate size, higher substrate temperatures and lower sputter gas pressures have a similar influence on the film structure and lead to more robust and etch-resistant films. Showing excellent light scattering properties, amorphous silicon pin solar cells prepared on these large area glass/ZnO samples exhibit initial efficiencies up to 9.2%, proving the viability of sputtered and texture-etched ZnO as TCO-substrate for industrial solar module production.