[stextbox id=”info”]Creating market barriers will lead to higher prices and less pressure for cost reduction and innovation, ultimately hurting the economies that adopt them[/stextbox]
Prof. Weber gave another example of a high-quality block-crystallised silicon material. There should be polarity switch in umg silicon. The umg Si is compensated: both boron (B) and phosphorous (P) are present in the feedstock. The dopant crossover is due to different segregation coefficients.The consequence: p- and n-type Si within the same brick and even single wafers. Dopant engineering is needed to avoid the p-n switch or increase the yield.
There is another example: non-conventional c-Si material or solar cells made from crystalline silicon thin-films. All concepts have good to very good cost perspective. High-throughput, low-cost Si deposition will be required for quick progress.
The key design data of a non-conventional c-Si material (ProConCVD) was presented. The ProConCVD is a massively scaled version of the ConCVD, intended to prove the scalability of the approach to a near-production level of more than a thousand wafers per hour. The data includes:
1. Three tracks, each with two car-riers. Each carrier holds three 156×156 mm2 wafers in height
2. Total deposition area: 5 m2
3. Maximum transport speed: 12 m/h
4. Furnace: max. 360kW, resistance-heated, 2x8m2 footprint, 2m stable zone
5. Process temperature up to 1300°C
6. Available process gases (maximum consumption/min): SiHCl3 (300 gm), SiCl4 (500 gm), SiCl3(CH3) (300 gm), H2 (4000 sl), HCl (50 sl)
7. Throughput > 30 m2/h (equivalent to 1200 wafers per hour) for 20μm layer thickness. A simple scale-up is possible.
As per the current status of ProConCVD, all hardware installations have been completed. The transport and heating system is in operation. The infrastructure is online. The firsthigh-quality epitaxial layers have been done successfully. Strategies to increase the efficiency o normal crystalline silicon solar cells include advanced metallisation, selective emitters, dielectric surface passivation, thinner wafers, process control, ultra-light trapping, material quality and back-contact cells. Estimating the efficiencypotential on boron-doped Cz-Si, with a limitation due to metastable boron-oxygen defect, there is the optimised industrial cell structure (PERL). The efficiencyis limited to about 20 per cent due to boron oxygen lifetime degradation. The solution: n-type silicon, with no degradation and higher tolerance to metal contamination.
The lab results of high-efficiency n-type PERL cells were also shared. There was substitution of local phosphorus diffusion by laser doping from innovative double-function PassDop layer (passivation and doping). Excellent results were achieved with evaporated front contacts.
Prof. Weber talked about the efficiencies of Ni/CuSn metallisation. Solar cell properties include direct plating, lowly doped emitter (120 ohms/square) and dielectric rear passivation. It also has excellent efficiecies and fillfactors. As for the thin-filmCIS solar cell structure, the key challenge is to realise the impressive small-area lab effciency results in production-size modules and volume production.
He touched upon the benefits of multi-junction sola cells and high-efficiencyISE triple-junction solar cells obtained by MOCVD thin-filmdeposition. Advantages of high-concentration PV cells include system effiiencies of 25 per cent AC today, about 200 MW/year worldwide production capacity, no cooling water or intentional hot water, modular kW to GW scale, and one-year energy payback time.
The future vision: Renewable electricity super grid
Prof. Weber gave an example of DESERTEC—the vision of an electricity super grid. DESERTEC is a mega renewable energy project that aims to set up a massive network of solar and wind farms stretching across the Middle East and North Africa (MENA) region and connected to Europe via a Euro-Mediterranean electricity network made up of high-voltage direct current transmission cables. The project, estimated at €400 billion, will provide 15 per cent of Europe’s electricity by 2050.
The author is an executive editor at EFY