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OPTIMIZATION OF HIGH EFFICIENCY MULTILAYER SOLAR CELLS BASED ON III/V COMPOUNDS.

Objective

THE OBJECTIVE OF OUR ACTIVITIES IS TWOFOLD. THE FIRST IMPORTANT ISSUE IS THE MATERIAL CHARACTERIZATION, MAINLY BY SIMS IN ORDER TO OPTIMIZE THE QUALITY OF EPITAXIALLY GROWN LAYERS. THE SECOND AIM IS THE IMPROVEMENT OF HETEROFACE SOLAR CELL PERFORMANCE. VERY GOOD RESULTS HAVE BEEN OBTAINED IN BOTH AREA'S
The research studied the characterisation of materials, mainly by secondary ion mass spectroscopy (SIMS), with the aims of optimising the quality of epitaxially grown layers and the improvement of heterophase solar cell performance.

We developed a simulation program to calculate the theoretical spectral response curves of various structures. By changing the structural conditions of the layers to be grown, a prediction of solar cell performance can be made. We calculated the effect of a reflecting mirror grown by molecular beam epitaxy (MBE) in the buffer layer of a solar cell as a function of emitter thickness, base thickness and aluminium gallium arsenide (AlGaAs) window conditions.
APPART FROM A SUPPORTING TASK OF THE ANALYSES APPARATURE, AN IMPROVEMENT OF THE DETECTION LIMIT FOR OXYGEN IN BULK MATERIAL HAS BEEN OBTAINED FOR BOTH ALGAAS (1X10 E17 CM-E3) AND GAAS (5X10 E17CM-E3) LAYERS.
THREE DIFFERENT ASPECTS ARE INVOLVED IN THE ACHIEVEMENT OF THE SECOND ACTIVITY: SOLAR CELL STRUCTURE DESIGN, IMPROVEMENT OF EPITAXIAL MATERIAL QUALITY AND PROCESSING. ALTHOUGH WE HAVE BEEN MODELING SOLAR CELL PERFORMANCE USING DEVICE SIMULATION PROGRAMS TO CLARIFY THE MERITS OF VARIOUS DESIGNS, THE IMPORTANT IMPROVEMENTS WE HAVE MADE WERE A CONSEQUENCE OF CAREFULL PROCESSING. BESIDES A HIGHER MATERIAL QUALITY WE INDEED DEVELLOPED A BETTER FABRICATION TECHNIQUE, ESPECIALLY FOR THE ANTI-REFLECTION COATINGS. THE SOLAR CELLS ARE GROWN BY MBE ON A 2 INCH GAAS WAFER. THE BASIC CELL STRUCTURE CONSISTS OF AN N+ EMITTER ON A P-TYPE BASE. THE THICKNESS OF THE EMITTER IS 400 NM, THE BASE CONSISTS OF TWO DIFFERENTLY DOPED P AND P+ TYPE GAAS LAYERS EACH 2 "MU" THICK. THE HEAVILY DOPED BUFFER LAYER SERVES AS A MINORITY CARRIER MIRROR. THE THICKNESS OF THE WIDE GAP A1 0.9GA 0.1 AS WINDOW LAYER IS REDUCED TO 50 NM AND CAN EVEN BE MADE THINNER TO AVOID ABSORPTION OF PHOTONS WITH AN ENERGY VALUE ABOVE 2 EV AS IS CLEAR FORM THE BUMP IN THE SPECTRAL RESPONSE CURVE. THE BEST CELL WITH AN AREA OF 0.43 CM2 REACHED AN EFFICIENCY OF 21.5 %.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

INTERUNIVERSITAIR MIKRO-ELEKTRONICA CENTRUM VZW
Address
75,Kapeldreef 75
3001 Heverlee
Belgium