Performance Analysis of Graded Bandgap p-i-n Junction Solar Cell

Abstract

A graded bandgap p-i-n junction solar cell is proposed. The main purpose of graded bandgap is to ensure more efficient absorption of photons. The efficiency will increase according to the load current. Here we use quaternary semiconductor material GaInAsP because it is easy to change the bandgap of this material without changing the lattice constant and we can change the bandgap over a wide region by changing their compositions. We have performed numerical calculation for energy gap and lattice parameter by changing the composition of the materials. From the compositions we get the maximum band gap 1.3723eV that we have to put on the top of the p-i-n solar cell, because the high frequency photon's penetration depth is low. Then we put an intrinsic material between p and n type doped material (here we use intrinsic material as graded GaxInl-xAsl-yPy and which is not doped at all). Finally at the bottom we put n-type material of minimum band gap 0.5135 eV. We allow ±0.05 % mismatch in lattice parameter between InP substrate and our active materials. We assumed the parameters such as effective density of states in the conduction band and valance band as independent of the bandgap. Assumed total number of electrons and holes are same and the reflectivity of sunlight for short circuit current calculation is neglected in the model. In this model the short circuit current, open circuit voltage, fill factor and finally efficiency are calculated. And efficiency of our designed graded bandgap p-i-n junction solar cell is around 18.42%. This value is for one sun concentration of sunlight. According to our efficiency it is expected that the proposed model can be used for better efficiency rather than other same category solar cells.