Growth and characterisation of sputtered transparent conducting oxides targeting improved solar cell efficiency

Transparent conducting oxides (TCO) are used to improve lateral current collection in thin film solar cells while allowing light into the absorber layers. Sputtering, an industrially mature coating technology, is potentially useful for low cost production of high quality TCO films. ZnO:Al films were grown by reactive MF (mid frequency) dual cathode magnetron sputtering from Zn:Al targets on glass with dynamic deposition rates up to 115 nm.m.minˉ¹ compared to 6 nm.m.minˉ¹ by RF sputtering from a single ceramic target. Adjusting the distribution of the oxygen influx improved the uniformity of the thickness and resistivity of ZnO:Al films grown on substrates measuring 30 cm × 30 cm. The ZnO:Al films were texture-etched for light trapping in micro-crystalline silicon (μc-Si:H) solar cells. Optimally textured ZnO:Al films were used as front contacts in 1 cm² single junction μc-Si:H solar cells yielding an initial efficiency of 8.4 % which is comparable to cells on textured RF sputtered ZnO:Al films, despite the much higher deposition rate. [Continues.

A Techno-Economic Perspective on Solar-to-Hydrogen Concepts through 2025

The transition towards a renewable energy-based society is challenged by spatial and temporal imbalances of energy demand and supply. Storage properties and versatility may favor hydrogen to serve as the linking element between renewable energy generation and a variety of sector coupling options. This paper examines four alternative solar-based hydrogen production concepts based on concentrated solar (CSP) or photovoltaic (PV) power generation and solid oxide (SOE) or polymer electrolyte membrane (PEM) electrolysis, namely, CSP-SOE and CSP-PEM, as well as PV-PEM concepts with (PV-PEM I) or without (PV-PEM II) power converters coupling both devices. In this paper, we analyze these concepts in terms of their techno-economic performance in order to determine the levelized cost of hydrogen (LCOH) for the target year 2025, based on different locations with different climate conditions. The analysis was carried out using a broadly applicable computer model based on an hourly resolved time-series of temperature and irradiance. The lowest LCOH was identified in the case of the CSP-SOE and CSP-PEM concepts with 14–17 €-ct per kW per h at high-irradiance locations, which clearly exceed the US Department of Energy (DOE) target of 6 $-ct per kW per h for the year 2020. Moreover, CSP-SOE also shows the highest hydrogen production volumes and, therefore, solar-to-hydrogen efficiencies. Considering the PV-PEM concepts, we found that the application of power converters for the electrical coupling of PV modules and electrolyzers does not contribute to cost reduction due to the higher related investment costs. A further system optimization is suggested regarding the implementation of short-term energy storage, which might be particularly relevant at locations with higher fluctuations in power supply

Light Scattering and Current Enhancement for Microcrystalline Silicon Thin-Film Solar Cells on Aluminium-Induced Texture Glass Superstrates with Double Texture

Microcrystalline silicon (μc-Si:H) thin-film solar cells are processed on glass superstrates having both micro- and nanoscale surface textures. The microscale texture is realised at the glass surface, using the aluminium-induced texturing (AIT) method, which is an industrially feasible process enabling a wide range of surface feature sizes (i.e., 700 nm–3 μm) of the textured glass. The nanoscale texture is made by conventional acid etching of the sputter-deposited transparent conductive oxide (TCO). The influence of the resulting “double texture” on the optical scattering is investigated by means of atomic force microscopy (AFM) (studying the surface topology), haze measurements (studying scattering into air), and short-circuit current enhancement measurements (studying scattering into silicon). A predicted enhanced optical scattering efficiency is experimentally proven by a short-circuit current enhancement ΔIsc of up to 1.6 mA/cm2 (7.7% relative increase) compared to solar cells fabricated on a standard superstrate, that is, planar glass covered with nanotextured TCO. Enhancing the autocorrelation length (or feature size) of the AIT superstrates might have the large potential to improve the μc-Si:H thin-film solar cell efficiency, by reducing the shunting probability of the device while maintaining a high optical scattering performance

Dye-sensitised solar cells using high mobility, transparent conducting oxides for tandem solar cell applications

Dye-sensitised solar cells are suitable for use as a top cell in a tandem solar cell structure, with a bottom CIGS solar cell, because their transmission characteristics can be adjusted by changing the particle size of the mesoporous TiO2 layer, and the photosensitising dye used. However, optical losses also occur from the fluorine doped tin oxide electrode, due to free carrier absorption in the NIR region of the solar spectrum, and lower the light available to the bottom cell. To solve this problem, a high mobility transparent conducting oxide (titanium doped indium oxide) has been used as the conducting layer to lower the optical loses in the near infrared through the cell. This increases light transmission from 800nm onwards, whilst maintaining high conductivity in the layer, which could be used in a tandem device. A device efficiency of 6.77% has been fabricated, whilst problems of porous layer delamination, and low temperature stability of the conducting layer have been solved