Efficient Nanostructured Silicon (Black Silicon) PV Devices
Antireflective (AR) coatings on solar cells increase the efficiency of the cells by suppressing reflection, which allows more photons to enter a silicon (Si) wafer and increases the flow of electricity. Traditional AR coatings however, add significant cost to the solar cell manufacturing process. NREL scientists have devised a method and created a nanostructured Si wafer, or black Si, which eliminates the need for a traditional AR coating while achieving comparable or higher solar cell efficiencies, and can be easily integrated with current production processes.
To date, nanostructured Si has had lower efficiencies than standard interference-based AR coatings due to poor spectral response at short wavelengths. By controlling the size of the nanostructures, the doping profile of the emitter and the amount of recombination metal atoms in the emitter in the nanostructured Si, NREL scientists have achieved a nanostructured, “black” Si. Solar cells incorporating black Si exhibit greater than 18% efficiency with internal quantum efficiency above 50% at 400 nm. The process can be used for mono-crystalline and multi-crystalline Si wafers or films with various thicknesses from 2 – 300 µm and p-type or n-type base. The concept can also be applied to detectors made of silicon, in order to make them more sensitive to blue light.Description
Nanostructured Si provides excellent optical properties, such as broad-band anti-reflection without the need for heterogeneous coatings, which can be used in photovoltaics with significant economic benefit. When these nanostructures are adopted in solar cells, however, nanostructured Si solar cells have been shown poor efficiency when compared to solar cells with industry standard AR coatings. The limited performances of the nanostructured Si cells are thought to arise from the poor spectral response of at short wavelengths from increased surface area and other associated device-structural issues.
NREL researchers have devised with an innovative way to integrate nanostructured Si into solar cells, which introduces three key aspects to the integration process. The first aspect is based on the optimized lateral feature sizes for effective suppression of reflectance and optimized surface area. The second aspect utilizes a specific low doping level in the nanostructured emitter to minimize Auger recombination, while still providing high VOC. The third aspect is the use of a nanostructure formation process that does not leave high recombination metal atoms in the emitter.NREL researchers have demonstrated a nanoporous, black Si solar cell with excellent spectral response at short wavelengths and superior overall power conversion efficiency of 18.2%. This improved performance was achieved by reduced surface area and removal of very heavily doped surface of the black Si after emitter formation.BenefitsIncrease in efficiency, antireflective coating improvementsApplications and IndustriesPV manufacturing, silicon detectors, silicon inks,More InformationWIPO Publication No. WO/2012/121706
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|NREL ROI 11-43||Production||Available||01/08/2013||01/08/2013|