Development of Some Alternative Chalcogenide Materials, Thin Films and Diodes for Fabrication of Low Cost Solar Cells

Abstract

There has been an immense interest in the development of alternatives materials and fabricate electronic devices which provide affordable solar energy generation as well as opto electronic energy transformation applications. Lot of efforts has, therefore, been put in to explore cost- effective, non-toxic and abundant materials. Chalcogenide materials quite recently have attracted attention particularly in the thin film technology due to their applications as non-linear optical materials, infrared sensors and solar energy convertors. Tin chalcogenide Sn(S,Se,Te) binary and ternary materials offer a wide range of optical band gaps suitable for various optical and optoelectronic applications. These materials have exhibited flexibility to possess variable band gaps which are suitable to tap different regions of solar spectrum which have made these materials as potential candidates for applications in photovoltaic solar cell devices. Besides, these materials have also been used as sensor and laser applications, thin film polarizer and thermo electric materials.The work to be presented in the meeting has been focused at the analysis of some Sn(S,Se,Te) binary and ternary thin films for their use as absorber layer in solar cell fabrications. The emphasis shall be made to analyze the change in the band gap, resistivity, absorption coefficient of the undertaken materials and thin films with variation in their elemental compositions and crystal structures. The undertaken materials and thin films were analyzed on the basis of structural, morphological, electrical and optical properties. SnSe and SnS demonstrated orthorhombic crystal structure while SnSe2 possessed hexagonal structure. SnTeSe, however, showed transition from hexagonal to orthorhombic crystal structures with increase in the substrate temperature from 300K to 550K. The electrical and optical analysis of the undertaken films showed change in the optical band gap, resistivity and absorption coefficient values. The films exhibited band gap energies spanning from the visible to near infrared regions. The Schottky barrier diodes of the deposited films were formed and their characteristics analyzed for the temperature dependent current voltage (I-V) and capacitance voltage (C-V) behavior. The current-voltage and capacitance-voltage characteristics of the diodes confirmed that the diodes formed on the deposited films are of good quality. The ideality factors decreased and barrier heights increased with increase in the substrate temperatures in all diodes. The temperature dependence of the barrier heights and ideality factors has been explained on the basis of “barrier inhomogenities” existing over the interface. Further, the variations between the experimentally observed values to the theoretically generated values have been explained on the basis of Gaussian distribution function which indicated the possibility of the presence of the tunneling current component in the electrical transport mechanism existing over the interface. The breakdown voltage phenomenon in the undertaken diodes provided negative temperature coefficient and depicted soft breakdown due to “defect assisted tunneling” over the interface.