Enhanced efficiency of Schottky-barrier solar cell with periodically nonhomogeneous indium gallium nitride layer

Tom H Anderson,Tom G Mackay,Akhlesh Lakhtakia

doi:10.1117/1.jpe.7.014502

Abstract

A two-dimensional finite-element model was developed to simulate the optoelectronic performance of a Schottky-barrier solar cell. The heart of this solar cell is a junction between a metal and a layer of n-doped indium gallium nitride (InξGa1−ξN) alloy sandwiched between a reflection-reducing front window and a periodically corrugated metallic back reflector. The bandgap of the InξGa1−ξN layer was varied periodically in the thickness direction by varying the parameter ξ∈(0,1). First, the frequency-domain Maxwell postulates were solved to determine the spatial profile of photon absorption and, thus, the generation of electron–hole pairs. The AM1.5G solar spectrum was taken to represent the incident solar flux. Next, the drift-diffusion equations were solved for the steady-state electron and hole densities. Numerical results indicate that a corrugated back reflector of a period of 600 nm is optimal for photon absorption when the InξGa1−ξN layer is homogeneous. The efficiency of a solar cell with a periodically nonhomogeneous InξGa1−ξN layer may be higher by as much as 26.8% compared to the analogous solar cell with a homogeneous InξGa1−ξN layer.

Highlights

A variety of light-trapping strategies capitalizing on structures engineered on the order of the wavelength of solar light have been examined both experimentally and theoretically to enhance the efficiencies of solar cells.[1]
It was demonstrated that the incorporation of a periodically nonhomogeneous intrinsic layer (i.e., i layer), along with a periodically corrugated back reflector, in amorphous silicon p-i-n junction solar cells can improve overall efficiency by up to 17%
I. the periodic corrugation of the metallic back reflector[4,5,6,17] facilitating the excitation of surface-plasmon-polariton waves[18,19,20] and waveguide modes[21] to intensify the electric field inside the semiconductor region, leading to an increase in the electron–hole pair (EHP) generation rate; ii. the periodic nonhomogeneity of the i-layer that may facilitate the excitation of multiple surface-plasmon-polariton waves[22] and waveguide modes,[17] thereby further boosting the EHP generation rate; and iii. the accompanying spatial gradient in the bandgap that may aid charge separation and reduce the EHP recombination rate.[23,24]

Summary

Introduction

A variety of light-trapping strategies capitalizing on structures engineered on the order of the wavelength of solar light have been examined both experimentally and theoretically to enhance the efficiencies of solar cells.[1]. It was demonstrated that the incorporation of a periodically nonhomogeneous intrinsic layer (i.e., i layer), along with a periodically corrugated back reflector, in amorphous silicon p-i-n junction solar cells can improve overall efficiency by up to 17%.16. When the proportion of indium is large (i.e., ξ ≳ 0.3), poor crystal growth plagues the realization of solar-cell applications Such poor growth results in decreased carrier transport, background n doping due to Fermi pinning above the conduction band edge,[34] and a bandgap that is greater than expected.[35,36] By using a Schottky-barrier junction with n-doped InξGa1−ξN, as opposed to a p-i-n junction, the difficulty of p doping the material is avoided.

Physical Model

Computational Model

Design of Periodically Corrugated Back Reflector

Findings

Closing Remarks