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Content archived on 2024-04-15

NARROW BAND-GAP ALLOYS FOR THE IMPROVEMENT OF EFFICIENCY OF AMORPHOUS SILICON-BASED SOLAR CELLS

Objective

THIS RESEARCH WORK UNDERTAKEN IN SEVERAL FRENCH LABORATORIES IS DIRECTED TOWARD THE IMPROVEMENT OF THE EFFECIENCY OF THIN FILM SOLAR CELLS.

THE RESEARCH IS ESSENTIALLY AIMED AT PREPARING DEVICE-QUALITY SIGE ALLOYS. ALLOYS WERE SYNTHESIZED IN THE GLOW DISCHARGE ARCAM REACTOR FROM SIH4:GEH4:H2. TWO DIFFERENT TECHNIQUES WERE INVESTIGATED: THE HYDROGEN DILUTION METHOD AND THE ION BOMBARDMENT METHOD. THE FIRST ONE CONSISTS IN SATURING WITH HYDROGEN THE GROWING SURFACE OF THE FILM TO DECREASE THE STICKING COEFFICIENT OF THE IMPINGING SPECIES THUS ALLOWING RELAXATIONS TO ENERGETICALLY FAVORABLE SITES. THE SECOND ONE CONSISTS IN TAKING ADVANTAGES OF THE ION MOMENTUM TRANSFER TO THE REACTIVE SPECIES ADSORBING ON THE GROWING FILM SURFACE, WHILE AVOIDING ION INDUCED DAMAGE BY IMPLEMENTATION. IN OTHER WORDS, ION BOMBARDMENT AT A MODERATE ENERGY (50 EV) INDUCES A DRASTIC CHANGE OF THE FILM GROWTH PROCESS LEADING TO DENSIFICATION OF THE MATERIAL AND A MODIFICATION OF HYDROGEN INCORPORATION AND BONDING MODES. THE MOST INTERESTING RESULTS WERE OBTAINED FOR SPECIMENS PREPARED AT TS = 135 DEGEES CELCIUS. WHEN A PROGRESSIVELY NEGATIVE BIAS IS APPLIED NO CHANGE IN THE FILM COMPOSITION IS OBSERVED, BUT THE TAUC OPTICAL GAP IS DECREASED FROM 1.67 TO 1.45 EV (FIG.1) THE DEPOSITION RATE IS INCREASED, -SIH2 AND -(SIH2)N-BONDING CONFIGURATIONS ARE REDUCED AND THE PHOTOCONDUCTIVITY IS INCREASED (FIG.2). BOTH PREPARATION TECHNIQUES ALLOW TO PREPARE DEVICE-QUALITY ALLOYS HAVING THE FOLLOWING PHYSICAL PROPERTIES : 1.45-1.5 EV TAUC OPTICAL GAP, TOTAL SPIN DENSITY: 5 X 10E16 CM E-3, URBACH TAIL PARAMETER:50 MEV, SMALL IR ABSORPTION AT 2100CM E-1 AND SMALL CONCENTRATION OF WEAKLY BONDED HYDROGEN, PHOTOCONDUCTIVITY TO DARK PHOTOCONDUCTIVITY RATIO = 10E4. FUNDAMENTAL PHYSICAL STUDIES LIKE X-RAY DIFFRACTION, SOFT X-RAY ABSORPTION, ESR, TIME OF FLIGHT, CAPACITANCE AND PHOTOCONDUCTIVITY WERE CARRIED OUT ON THE OPTIMIZED MATERIALS. DEVICE STRUCTURES LIKE SCHOTTKY BARRIERS WERE ALSO STUDIED.

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Funding Scheme

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Coordinator

Centre National de la Recherche Scientifique (CNRS)
EU contribution
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Address

91405 Orsay
France

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Total cost

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