Prospects of Back Surface Field Effect in Ultra-Thin High-Efficiency CdS/CdTe Solar Cells from Numerical Modeling

Nowshad Amin,M M Aliyu,M R Karim,K Sopian,M A Matin,M A Alghoul

doi:10.1155/2010/578580

Abstract

Polycrystalline CdTe shows greater promises for the development of cost-effective, efficient, and reliable thin film solar cells. Results of numerical analysis using AMPS-1D simulator in exploring the possibility of ultrathin, high efficiency, and stable CdS/CdTe cells are presented. The conventional baseline case structure of CdS/CdTe cell has been explored with reduced CdTe absorber and CdS window layer thickness, where 1 μm thin CdTe and 50 nm CdS layers showed reasonable efficiencies over 15%. The viability of 1 μm CdTe absorber layer together with possible back surface field (BSF) layers to reduce minority carrier recombination loss at the back contact in ultra thin CdS/CdTe cells was investigated. Higher bandgap material like ZnTe and low bandgap materials like Sb2Te3and As2Te3as BSF were inserted to reduce the holes barrier height in the proposed ultra thin CdS/CdTe cells. The proposed structure of SnO2/Zn2SnO4/CdS/CdTe/As2Te3/Cu showed the highest conversion efficiency of 18.6% (Voc= 0.92 V,Jsc= 24.97 mA/cm2, and FF = 0.81). However, other proposed structures such as SnO2/Zn2SnO4/CdS/CdTe/Sb2Te3/Mo and SnO2/Zn2SnO4/CdS/CdTe/ZnTe/Al have also shown better stability at higher operating temperatures with acceptable efficiencies. Moreover, it was found that the cells normalized efficiency linearly decreased with the increased operating temperature with relatively lower gradient, which eventually indicates better stability of the proposed ultra thin CdS/CdTe cells.

Highlights

Over the period of recent decade, cadmium telluride (CdTe) has shown greater promise for efficient, low-cost photovoltaic (PV) solar cells
It is noteworthy that in most high efficiency CdS/CdTe solar cells, the CdTe absorber layer is purposely set at 5 μm and above to avoid pinhole formation and uniformity limitation
Further numerical analysis was done to reduce the thickness of CdTe and CdS layers aiming to conserve the materials usages and cost of cell production

Summary

Introduction

Over the period of recent decade, cadmium telluride (CdTe) has shown greater promise for efficient, low-cost photovoltaic (PV) solar cells. The lesser thickness required for an absorbing layer can lead to reduced cell material usage and lower cost of fabrication. As2Te3 is a p-type semiconductor which has a forbidden gap of about 0.6 eV and exhibits resistivity of 10−3 Ωcm at room temperature It melts at 360◦C and can evaporate at temperatures higher than 250◦C in vacuum; they have reported CdS/CdTe cell with efficiency of 15.8% using As2Te3 material. The strategies for improving CdS/CdTe cell output performance have been explored utilizing AMPS 1D (Analysis of Microelectronic and Photonic Structures) [11] simulator, and the obtained results are discussed This analysis has shown that SnO2/Zn2SnO4 front contact with Sb2Te3/Mo and As2Te3/Cu as BSF are suitable material system for higher efficiency (>17.2%) and stable ultra thin CdS/CdTe cells. The performances of the cell with ZnTe BSF have shown better overall stability than other cells

Experimental Modeling and Simulation

Results and Discussion

Conclusion