MULTIJUNCTION SOLAR CELL

Abstract

Multijunction (M-J) solar cell and Nanowire (NW) solar cell structures are the most favorable choice in today's photovoltaic research. These type of designs (structure) have shown good results in terms of performance, and the cost of manufacturing. Better absorption of light, improved charge separation, better collection of charge, large surface to volume ratio, low cost of manufacture and better defect tolerance are the main qualities of NW which makes it advantageous over conventional planar solar cell. M-J solar cells have been reported to have maximum efficiency. The main advantage of M-J solar cell is that, the range of bands of the solar spectrum which is absorbed is increased due to use of different bandgap materials. It is a good idea to devise methods and techniques to utilize this advantages of NW and M-J solar cells, to make a device by the combination of two. In this work the optimization of vertical GaAs p-i-n NW solar cell has been carried. Optimization of the structure gives us the values of the best possible structural parameters to give the best performance (efficiency) from the device. Effects of doping density, height, core radius, shell thickness and incidence light angle variation in NW structure are investigated. GaAs p-i-n nanowire solar cell have all the advantages of NW structure and shows promising results after optimization, which can be viewed in the simulation results as discussed in this report. Apart from the optimization of structure, the study of variation of incident angle of light suggest that efficiency can be further improved if the incident light is made to fall at certain angle with the nanowire axis. Study of incident angle shows that total internal reflection is possible in the NW structure. A M-J solar cell shows improved absorption of spectrum than a single junction solar cell. In this work structure of M-J vertical NW has been investigated. GaAs-silicon hetro-junction tunnel diode is optimized for higher tunnel current in order to use it in the simulation of M-J. A study of top NW cell height, bottom planar cell height, NW cell doping, planar cell doping, optimization of tunnel diode structure is investigated in this work. The resulting efficiency is marginally higher, when compared with the individual cells of GaAs NW and silicon planar cell, thus it is beneficial to make a M-J NW structured solar cell.