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GAAS THIN FILM SOLAR CELLS OBTAINED BY VAPOUR PHASE HOMOEPITAXY (VPE) ON REUSABLE SUBSTRATES.

Objective

AIM OF THIS WORK IS THE FABRICATION OF SINGLE CRYSTAL GAAS HOMOJUNCTION SOLAR CELLS, FEW MICROMETERS THIN WITH A CONVERSION EFFICIENCY SIMILAR TO THAT OF THICK DEVICES. MOREOVER THE FABRICATION PROCESS WILL ALLOW TO REUTILIZE THE SAME GAAS SUBSTRATE FOR SEVERAL TIMES GETTING A DRASTIC REDUCTION OF THE COSTS.

OUR APPROACH TOWARDS HIGH-EFFICIENCY LOW-COST SOLAR CELLS IS TO USE THIN FILM (5-10 UM) SINGLE-CRYSTAL GAAS SOLAR CELLS, FOLLOWING THE CLEFT APPROACH DEVELOPED AT MIT. THIS PROCESS, ALLOWING TO FABRICATE SEVERAL THIN FILM SINGLE-CRYSTAL GAAS SOLAR CELLS REUTILIZING THE SAME GAAS SUBSTRATE AFTER EACH RUN, IS BASED ON THE EPITAXIAL LATERAL OVERGROWTH OF GAAS LAYERS OVER PHOTOLITHOGRAPHICALLY MASKED MONOCRYSTALLINE SUBSTRATES, BY TAKING ADVANTAGE FROM THE DEPENDENCE OF THE GROWTH RATE ON THE CRYSTALLOGRAPHIC ORIENTATION IN THE ASCL3-GA VAPOUR PHASE EPITAXY (VPE). THE USE OF GAALAS AS TOP PASSIVATING LAYER IS NOT ALLOWED, THEREFORE P-N SHQLLOW HOMOJUNCTION DEVICES HAVE TO BE FABRICATED, WITHOUT AHMIC CONTACT THERMAL ALLOYING.
A VPE SYSTEM HAS BEEN DESIGNED, FABRICATED AND OPTIMIZED TO GROW P AND N-DOPED GAAS LAYERS WITH THE PROPER TRANSPORT PROPERTIES. SINCE THE MOST SUITABLE SUBSTRATES FOR THE CLEFT PROCESS ARE <110> ORIENTED (LATERAL TO VERTICAL GROWTH RATE RATIO = 10-20) THE GROWTH CONDITIONS ON THESE SUBSTRATES HAVE BEEN INVESTIGATED AND OPTIMIZED TOO.
THE TECHNOLOGY OF FABRICATION AND CLEAVING OF THIN GAAS FILMS FROM THE SUBSTRATE HAS BEEN SUCCESSFULLY ACHIEVED. THE BEST SHALLOW HOMOJUNCTION SOLAR CELL SHOWS A CONVERSION EFFICIENCY OF 15% (100 MW/SQCM, AM1.5), MAINLY LIMITED BY JSC (22 MA/SQCM), EVEN IF BOTH VOC (925 MV) AND FF (.73) CAN BE FURTHER IMPROVED.
OUR SUCCESSFUL RESULTS TOGETHER WITH THE VERY RECENT REALIZATION AT THE KOPIN CORP. OF BOTH 2" DIAMETER 10 UM THICK CELL MAKE VERY PROMISING THE CLEFT APPROACH AND ENCOURAGE US TO CONTINUE OUR RESEARCH ACTIVITY.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Ente per le Nuove Tecnologie l'Energia e l'Ambiente (ENEA)
Address
Via Vecchio Macello
80055 Portici Napoli
Italy