Ab-initio calculation study on the formation mechanism of boron-oxygen complexes in c-Si

Xuegong Yu,Peng Chen,Xianzi Chen,Deren Yang,Yong Liu

doi:10.1063/1.4927498

Abstract

Boron-oxygen (B-O) complex in crystalline silicon (c-Si) solar cells is responsible for the light-induced efficiency degradation of solar cell. However, the formation mechanism of B-O complex is not clear yet. By Ab-initio calculation, it is found that the stagger-type oxygen dimer (O2ist) should be the component of B-O complex, whose movement occurs through its structure reconfiguration at low temperature, instead of its long-distance diffusion. The O2ist can form two stable “latent centers” with the Bs, which are recombination-inactive. The latent centers can be evolved into the metastable recombination centers via their structure transformation in the presence of excess carriers. These results can well explain the formation behaviors of B-O complexes in c-Si.

Highlights

As standard p-type silicon solar cells are widely used in photovoltaics (PV), the well-known detrimental defects, boron-oxygen (BO) complexes which cause the light-induced efficiency degradation (LID) and electricity loss, have attracted intensive attention since the last decade
We suggest that the O2i tends to be captured by Bs atoms instead of Bi atoms to form the latent centers, and the LID process corresponds to the transformation of latent centers to recombination centers, without involving the long-range diffusion of O2i
Based on ab initio calculations, we have proposed a new BsO2i model to understand the properties of B-O complexes, such as their microstructures and formation mechanisms

Summary

Introduction

As standard p-type silicon solar cells are widely used in photovoltaics (PV), the well-known detrimental defects, boron-oxygen (BO) complexes which cause the light-induced efficiency degradation (LID) and electricity loss, have attracted intensive attention since the last decade. These complexes are readily to form once Si crystal simultaneously contains the dopant B and the inevitable impurity O incorporated by dissolving the silica crucible.[1] The complexes can form in the case of excess carrier injection under light illumination[2] or application of forward bias,[3] and can be fully annealed out at elevated temperatures in dark. Advanced carrier-lifetime spectroscopic studies have revealed that the slow-forming defect has a deep level at Ec-0.41 eV with capturing cross-section ratio σn/σp of 10 and a shallow level at Ec-0.15 eV with uncertain σn/σp value,[8,9,10] while the fast-forming defect is a deep center with energy level lying between Ec-0.35 and Ec-0.85 eV and with a much larger σn/σp of 100.6

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Conclusion