HETEROJUNCTION SOLAR CELLS

THE USE OF THIN POLYCRYSTALLINE FILMS OF DIRECT GAP SEMICONDUCTORS WITH ENERGY GAP IN THE RANGE OF 1.3-1.7 EV ON A SUITABLE SUBSTRATE IS BELIVED TO BE MOST PROMISING FOR THE FABRICATION OF LOW-COST SOLAR CELLS FOR TERRESTRIAL APPLICATIONS. BECAUSE OF THE DIFFICULTY OF OBTAINING SHALLOW HOMOJUNCTIONS WITH LOW SHEET RESISTANCE SURFACE LAYER IN MANY DIRECT GAP SEMICONDUCTORS, HETEROJUNCTION STRUCTURES ARE USED. THE HETEROJUNCTION PARTNER IS USUALLY A LARGE BAND GAP SEMICONDUCTOR WITH HIGH ELECTRICAL CONDUCTIVITY (THE WINDOW MATERIAL), SUCH AS CADMIUM SULFIDE, INDIUM TIN OXIDE, ZINC OXIDE, ETC. HETEROJUNCTION THIN FILM SOLAR CELLS, SUCH AS CADMIUM SULFIDE/COPPER INDIUM SELENIDE AND CADMIUM SULFIDE/CADMIUM TELLURIDE, WITH AML EFFICIENCIES HIGHER THAN 10% HAVE BEEN OBTAINED. ALL WINDOW MATERIALS ARE OF N-TYPE CONDUCTIVITY DUE TO NON-STOICHIOMETRY (ANION VACANCIES ARE DONORS) OR THE INTRODUCTION OF DOPANTS, THUS LIMITING THE SOLAR CELLS TO THE N(+)-WINDOW MATERIAL/P-TYPE SEMICONDUCTOR CONFIGURATION. SINCE THE USE OF AN N-TYPE SEMI-CONDUCTOR FILM IS MORE DESIRABLE DUE TO ITS SURFACE STABILITY AND THE EASE OF CONTACT FORMATION, P-TYPE WINDOW MATERIALS MUST BE DEVELOPED. THE OBJECTIVE OF THIS PROPOSAL IS TO DEVELOP P-TYPE WINDOW MATERIALS FOR HETEROJUNCTION SOLAR CELLS BY PLASMA ENHANCED CHEMICAL VAPOR DEPOSITION TECHNIQUE. BORON DOPED SILICON NITRIDE FILMS AND BORON-DOPED SILICON CARBIDE FILMS WILL BE DEPOSITED ON GLASS SUBSTRATES AT TEMPERATURES UP TO 300 DEGREES C. THE PROCESS PARAMETERS, PARTICULARLY COMPOSITION AND FLOW RATE OF THE REACTION MIXTURE AND RF POWER, WILL BE VARIED OVER A WIDE RANGE TO DETERMINE THEIR AFFECTS ON THE STRUCTURAL, OPTICAL, AND ELECTRICAL PROPERTIES OF DEPOSITED FILMS. THE STRUCTURAL, OPTICAL, AND ELECTRICAL PROPERTIES WILL BE MEASURED BY THE LOW-ANGLE LAUE SPECTROPHOTOMETRIC, AND POTENTIAL PROBE TECHNIQUES, RESPECTIVELY. THE FEASIBILITY OF PRODUCING P-TYPE WINDOW MATERIAL FOR HETEROJUNCTION THIN FILM SOLAR CELLS CAN THUS BE DETERMINED.