Study of electrical properties of a-Si:H Hetro-junction solar cells and metal-oxide nano-fibers based photo-anode for application in advance generation solar cells

Abstract

Increase in world energy crisis and depletion of conventional energy resources are some of the major issue the world is facing nowadays. To mitigate the utilization of conventional energy and to overcome these energy crises, alternate and sustainable energy resources are obligatory. One of the potential ways is to use renewable energy resources. Among Renewable energy resources, photo-voltaic technology is an efficient one because of the availability of surplus amount of solar light. Solar cells consist of 3 major generation based on the materials used for generation of electron-hole pair. Among 2nd generation solar cells, a-Si:H hetro-junction solar cells are an efficient type of solar cells that have currently obtained exceptional power conversion efficiency. But due high contact resistance on the surface of such solar cells, the theoretical efficiency has not been achieved yet. Similarly 3rd generation Dye-sensitized solar cells are among the top candidate for solar cells with easy and low cost for fabrication. Among various components of DSSC, photo-anode is one of the most dominant component for which various metal oxide nano-structures are used. These nano-structures include nano-particles, nano-rods and nano-fibres. Metal oxide nano-fibres are been currently used in DSSC as photo-anode to obtain large-surface area to volume ratio for better electron transport. Among these Titania is widely used but because of the issues like recombination of electron-hole pair, composite of Titania and other metal oxides is used. In this work, transfer length measurement (TLM) pattern cells were successfully prepared using PECVD and RF sputtering. Different layer of a-Si:H hetro-junction were varied to study their effects on contact resistance. TLM pattern consist of multiple spacing between metal contacts. The effect of varing p a-Si:H layer, varing i-layer thickness with no p- a-Si:H layer, effect of annealing temperature and TMB flow in PECVD chamber was studied. Similarly electrical properties of indium oxide (IO) were also studied as transparent conductive oxide (TCO), which shows that increase in sputtering time increases the thickness of the deposited film which results in the increase in mobility and decrease in sheet resistance under constant Ar, oxygen and vacuum. With change in oxygen concentration thickness and carrier concentration decreases but mobility increases because of formation of grain size defects. Likewise, TiO2 nano-fibres, SnO2 nano-fibres and TiO2-SnO2 nano-fibres by using Poly-vinyl pyrollidone were vi successfully synthesized using Electro-spinning for photo-anode of DSSC. Solution electro-spinning and co-axial electro-spinning was used to synthesize the fibers. The structural, optical and electrical properties of the prepared nano-fibres were carried out by the diversified techniques including X-ray diffraction, Scanning Electron microscopy, Fourier transform infrared spectroscopy, UV-VIS NIR spectrophotometer and Hall Effect measurement system. The effect of polymer concentration was studied which shows that with increase in polymer, the diameter of the fiber increases. The prepared TiO2-SnO2 film has more conductivity and have higher band-gap then bare TiO2 nano-fibres. More-over the prepared films were successfully sensitized by using graphene nano-platelets using Di-methyl formamide (DMF) as a solvent. Graphene sensitization not only increases the conductivity of the film but also increases the band-gap. One of the draw-back of graphene sensitized nano-fibers is that it gives absorption in UV- region.