The objective of 'OASIS' is to increase cost-effectiveness of PV modules based on amorphous silicon and to carry out fundamental research on new materials and devices with the potential for application in PV modules.
A collaboration has been formed to facilitate the transfer of amorphous silicon photovoltaic technology from laboratory to industry. During 2 years, top module power has increased from 16.8 Wp to 17.8 Wp, cost has decreased from 1.52 ECU/Wp to 1.35 ECU/Wp, and yield has increased from 60% to 85% due to optimization of the fabrication process.
A program was developed to model the performance of the cells. It was used to calculate the spectral response and internal collection efficiency of single junction cells with various interface defects, under different levels of illumination, and with the addition of a high reflecting back contact. A cheap and reliable back contact for amorphous silicon solar cells was developed by means of low temperature screen printing techniques, involving the development of new polymeric pastes.
New deposition techniques and plasma engineering of deposition systems were developed, and the production of transparent conducting oxide (TCO) layers optimized. Blocking layers were developed. Characteristics of the films were examined by X-ray diffraction and infrared spectroscopy. The interface between the TCO layer and the silicon p-layer was studied. It was found that a thin silicon oxide layer reduced deterioration of the interface, but significantly degraded the transparency.
A new ultra high voltage multichamber deposition system was used to fabricate single junction solar cells of conversion efficiency greater than 10%. The band gap profile of undoped amorphous hydrogenerated silicon carbide (a-SiC:H) was examined and a suitable dopart chosen.
Intrinsic graded gap heterostructures on the basis of amorphous hydrogenated silicon-germanium (a-Di(1-x)Ge(x):H) were studied with respect to solar cell performance. Improved performance was attributed to an improved absorption profile rather than to improved carrier collection induced by the driving force of the effective built in field through the grading. The suitability of boron trifl uoride doped amorphous silicon carbide as a window layer was investigated. The films exhibited optical and electrical properties similar to or better than conventionally doped p-type films.
The cells were tested for degradation with age. Over 221 days, degradation of 30% in output power was observed.
In order to increase the cost effectiveness of photovoltaic (PV) modules based on amorphous silicon research is being carried out into the optimization of amorphous silicon solar modules (OASIS). New materials and devices with the potential for application in PV modules are also being analysed. The targets for module active area efficiency and for cells at laboratory scale are 8.3% and 10% respectively.
At the start of the project the efficiency of the modules was 6% and 4.4% after degradation. The 10% goal has been realised on small areas. A 7% efficiency after degradation in industrial production seems possible.
The target for module active area efficiency is 8.3% and for cells at laboratory scale 10%. In agreement with these efficiencies the target for module cost is 1.0 Ecu/Wp. These targets will be realized by taking the following steps:
- Improvement of the present production process of Chronar France (production over 1 MW/Year) by implementation, after careful technical and economic analyses, of techniques developed in the partners Laboratories
- Carrying out research on materials with a graded bandgap, on devices containing layers with different bandgaps and on the electrical contacts of solar cells.
For the analyses all the partners will be involved in executing tasks requiring their specific expertise and facilities and include:
- Economic analysis of techniques considered for implementation
- Characterisation of the solar modules by measuring its electrical performance and stability.
- Characterisation of the different layers and interfaces of samples from all the partners by determining its structure, by depth profiling and by electrical and optical characterisation.
With the technical analyses and an extended computer program for the simulation of amorphous silicon based devices it is possible to relate process parameters, device parameters and the performance of modules and solar cells. These relations will be used to judge which techniques will be implemented for improvement of the modules and solar cells.
The main task of every partner concerns either the industrial implementation of a new technique under development in his laboratory or the investigation of a new material or technique for application in solar cells and with industrial potential.
Funding SchemeCSC - Cost-sharing contracts
5600 MB Eindhoven
3508 TA Utrecht
2825 Monte De Caparica