2D modelling of polycrystalline silicon thin film solar cells

A.-M Teodoreanu ,Christian Boit,Caspar Leendertz,Lars Korte,R Leihkauf ,F Friedrich

doi:10.1051/epjpv/2013017

Abstract

The influence of grain boundary (GB) properties on device parameters of polycrystalline silicon (poly-Si) thin film solar cells is investigated by two-dimensional device simulation. A realistic poly-Si thin film model cell composed of antireflection layer, (n + )-type emitter, thick p -type absorber, and (p + )-type back surface field was created. The absorber consists of a low-defect crystalline Si grain with an adjacent highly defective grain boundary layer. The performances of a reference cell without GB, one with n -type and one with p -type GB, respectively, are compared. The doping concentration and defect density at the GB are varied. It is shown that the impact of the grain boundary on the poly-Si cell is twofold: a local potential barrier is created at the GB, and a part of the photogenerated current flows within the GB. Regarding the cell performance, a highly doped n -type GB is less critical in terms of the cell’s short circuit current than a highly doped p -type GB, but more detrimental in terms of the cell’s open circuit voltage and fill factor.

Highlights

IntroductionPolycrystalline silicon (poly-Si) is an attractive absorber material for thin film solar cells
Polycrystalline silicon is an attractive absorber material for thin film solar cells
The influence of grain boundary (GB) properties on device parameters of polycrystalline silicon thin film solar cells is investigated by two-dimensional device simulation

Summary

Introduction

Polycrystalline silicon (poly-Si) is an attractive absorber material for thin film solar cells. The best poly-Si thin film solar cells today show significantly lower efficiencies of 10.4% [4] and record VOCs of up to 582 mV [5,6,7], depending on the poly-Si material manufacturing method and contacting scheme. This demonstrates that there is a need and a potential of improvement of the poly-Si material. A basic 2D model of the poly-Si thin film solar cell was developed consisting of a low-defect crystalline grain and a highly defective grain boundary layer. While the influence of the GB doping type is ambivalent dependent on the parameter range, the cell’s VOC in general deteriorates in the presence of a GB

Modelling approach

Simulation results

Findings

Discussion

Conclusions and outlook