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MEASUREMENT OF THE ELECTRIC POTENTIAL AT THE FRATURE EDGE OF A P-I-N JUNCTION EMPLOYING ELECTRON BEAM TECHNIQUES.

Objective

ESTABLISH THE SCIENTIFIC AND TECHNICAL BASIS FOR A VIABLE EUROPEAN AMORPHOUS SILICON SOLAR CELL INDUSTRY.

THE DEVELOPMENT OF HIGH-EFFICIENCY A-SI SOLAR CELLS COULD BE ADVANCED BY EXAMINING THE POTENTIAL DISTRIBUTION ACROSS THE P-I-N JUNCTION ON WHICH THE EFFICIENCY IS KNOWN TO DEPEND. THE MEASUREMENT OF THE SURFACE POTENTIAL DISTRIBUTION ACROSS A FRACTURE EDGE OF THE P-I-N DEVICE PROMISES A SIMILAR BENEFIT. ELECTRON BEAM TESTING TECHNIQUES WHICH CAN PROVIDE HIGH SPATIAL RESOLUTION AND PRECISE SURFACE POTENTIAL MEASUREMENT WILL BE EMPLOYED IN ORDER TO OBTAIN THAT WAY THE INTERNAL ELECTRIC FIELD OF A P-I-N SOLAR CELL. THE PROPOSED TECHNIQUES CAN BE EXPECTED TO MEET THE REQUIREMENTS OF A LATERAL RESOLUTION OF 0.1 MICROMETRE AND A VOLTAGE RESOLUTION OF 0.1 V.

THE MAGNETICALLY FOCUSSED ELECTRON PROBE WILL BE SCANNED ACROSS THE APPROPRIATELY PREPARED FRACTURE EDGE OF THE DEVICE AND THE ELECTRONS RELEASED FROM THE SAMPLE WILL BE COLLECTED AND ANALYZED IN ORDER TO OBTAIN THE LOCAL POTENTIAL AT THE SURFACE FROM WHERE THE ELECTRONS STARTED. THE USE OF A SPECIALLY DESIGNED SINGLE POLE LENS BELOW THE SPECIMEN APPEARS TO BE A MOST PROMISING APPROACH.
FRACTURE EDGES OF A-SI P-I-N JUNCTIONS ON GLASS SUBSTRATE AND, FOR COMPARISON, OF COMMERCIAL C-SI CELLS AND PC-SI CELLS HAVE BEEN PREPARED AND WERE STUDIED BY SEM TECHNIQUES WITH RESPECT TO TOPOLOGICAL SMOOTHNESS, BECAUSE IRREGULAR TOPOGRAPHICAL CONTRAST MAY OVERRIDE ANY POTENTIAL CONTRAST. SMOOTHING THE FRACTURE EDGE OF C-SI CELLS BY APPLYING DIAMOND POLISHING PASTE SIGNIFICANTLY REDUCED THE UNWANTED STRUCTURES. FOR THIN A-SI P-I-N CELLS, OPTICAL POLISHING USING A CERIUM OXIDE SUSPENSION WAS PERFORMED AT VERY FLAT TILT ANGLES WITH RESPECT TO TETHE LAYER SURFACE. FOR FEASIBILITY DEMONSTRATION, FIRST POTENTIAL MEASUREMENTS ACROSS THE POLISHED FRACTURE EDGE OF A PC-SI CELL WERE CARRIED OUT BY USING A COMMERCIAL ELECTRON-BEAM TESTER. IN ORDER TO OVERCOME THE LIMITATIONS OF VOLTAGE AND SPATIAL RESOLUTION, AT FIRST A REVERSE BIAS VOLTAGE WAS APPLIED TO THE SAMPLE. WITH INCREASED BIAS VOLTAGE A BROADENING OF THE P-N JUNCTION WAS OBSERVED IN THE POTENTIAL MEASUREMENTS, IN QUALITATIVE AGREEMENT WITH THEORY.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

TECHNISCHE UNIVERSITAET KAISERSLAUTERN
Address
Erwin Schroedinger Strasse 46
67663 Kaiserslautern
Germany

Participants (3)

IMEC
Belgium
Messerschmitt-Bölkow-Blohm GmbH (MBB)
Germany
Address

81611 München
Solems SA
France
Address
3 Rue Léon Blum Zone Industrielle Les Glaises
91124 Palaiseau