Ziel
IN THE FRAME OF THE MBB-SOLEMS PROJECT ON THE DEVELOPMENT OF THE SCIENTIFIC AND TECHNICAL BASIS FOR A-SI MODULES, IMEC WILL FOCUS ON THE OPTICAL AND ELECTRICAL IMPROVEMENT OF THE DEVICE STRUCTURE.
Homo-chemical vapour deposition (CVD) amorphous silicon hydrogen thin films have superior photoluminescence and stability properties. In addition, strongly boron doped layers exhibit thickness independent conductivity.
The Homo CVD technique has been developed as a possible alternative for the deposition of the p+ window layer in a-Si solar cells. This is a very low substrate temperature (TS=80C) ion free deposition method which is expected to lead to a reduced interaction with the TCO and improved interfaces. It has been shown that good quality a-Si:H is obtained at reasonable growth rates (100 A/min) with superior photoluminescence properties.
THE CONTACT RESISTANCE OF LOW TEMPERATURE SCREENPRINTED CONTACTS ON A-SI PIN SOLAR CELLS STRONGLY DEPENDS ON THE CONDUCTIVITY OF THE UNDERLYING N+ GDMU-SI LAYER. A ROOM TEMPERATURE CONDUCTIVITY OF 5-10 (ONEGA CM) -1 IS NEEDED FOR RC<1ONGEGA CM2. VALUES AS LOW AS 10-1ONEGA CM2 HAVE BEEN OBTAINED FOR MO/AG PASTES. ON 8% EFFICIENT PIN SOLAR CELLS A FF OF 0.65 HAS BEEN OBTAINED WITH SCREENPRINTED CONTACTS AS COMPARED TO 0.70 WITH CONVENTIONAL EVAPORATED CONTACTS, INDICATING VERY SIMILAR EFFICIENCIES FOR BOTH METHODS. P-TYPE DOPING HAS BEEN ACHIEVED WITH THE HOMO-CVD METHOD AT TS=80 C AND THE OPTOELECTRONIC PROPERTIES OF THESE LAYERS DO NOT SEEM TO DEPEND ON FILM THICKNESS, IN CONTRAST WITH CONVENTIONAL GLOW DISCHARGE SIC THIN FILMS. THE STAEBLER-WRONSKI EFFECT IS LESS PRONOUNCED IN HOMO-CVD MATERIAL THAN IN COMPARABLE GD FILMS.
SELF-ANNEALING EFFECTS AND ROOM TEMPERATURE RECOVERY OF OPH HAVE BEEN OBSERVED AS WELL AS A HIGHER PHOTOLUMINESCENCE RESPONSE, INDICATING PROPERTIES SUPERIOR TO CONVENTIONAL GD P+ SIC THIN FILMS. IN COLLABORATION WITH THE UNIVERSITY OF LISBON, THE STRUCTURAL AND OPTOELECTRONIC PROPERTIES OF P- AND N-DOPED SIC FILMS PREPARED IN A TCDDC SYSTEM HAVE BEEN STUDIED. THIS WEAKLY ABSORBING HIGHLY CONDUCTIVE MATERIAL, WHICH PRESENTS AN INTERESTING ALTERNATIVE FOR THE A-SI SOLAR CELL WINDOW AND BACK LAYERS, CONSISTS OF SI MICROCRYSTALS, PROVIDING THE CONDUCTION PATH, EMBEDDED IN AN AMORPHOUS SI:C:O:H MATRIX.
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