PECVD System for 30×30 cm² Substrates
Motivation and Objectives
The scale-up of the PECVD technique for silicon thin-film solar cells from the laboratory scale (typical substrate size 10×10 cm²) to industrial manufacturing (~ m²) requires answers to be found to many scientific and technological questions regarding film thickness and optoelectronic properties in order to be able to produce homogeneous amorphous (a-Si:H) and microcrystalline (µc-Si:H) silicon films on a large area at a high rate. One central objective of our PEVCD development is to solve these problems for 30×30 cm² substrates in close cooperation with industry partners and thus to lay the foundations for cost-effective industrial manufacturing processes. The variable system design also facilitates the development of new PECVD processes and studies regarding the connections between deposition parameters, plasma properties and the growth of different silicon films.
The PECVD system consists of two load chambers and two deposition chambers – one for p- or n-doped silicon films and one for intrinsic a-Si:H and µc-Si:H absorber films. The basic version was supplied by MRG Inc. (Colorado, USA). The system was further equipped and optimized at IPV. The PECVD electrodes were developed within the framework of a cooperation between FAP GmbH (Dresden, Germany) and IPV. The electrodes can be operated at RF and VHF frequencies (13.56 MHz, 27.12 MHz and 40.68 MHz). The maximum base pressure of the system is 1×10-8 mbar. Plasma analyses for process control can be carried out during the production of intrinsic silicon films by means of optical plasma emission spectroscopy. These plasma diagnostics were developed at the 5‑chamber system for small areas and then adapted for the coating of larger areas.
Current Research Topics
The development and scale-up of PECVD processes aims at producing a-Si/µc-Si tandem solar cells with high stable efficiencies. The intrinsic a-Si:H and µc-Si:H absorber films are planned to be deposited at high rates. Promising lab developments are transferred to pilot production runs, production lines or system development at industry partners (Cooperations).
At the same time, the system provides reproducible standard processes for amorphous and microcrystalline silicon thin-film solar cells. These processes can be used to verify and examine the influence of changes in the cell process or other components. The system is thus integrated in the further development of TCO films, back reflectors and other components of the solar cell.