Structure and transformation of the metastable centre in Cz-silicon solar cells

摘要

In order to reveal the core structure of the performance-limiting metastable defect centre in czochralski-silicon (Cz-Si) solar cells, the quantitative correlation of the defect concentration with the boron and the oxygen contents is investigated on a large number of different Cz-Si materials. The experimental results indicate that the defect is composed of one substitutional boron and two interstitial oxygen atoms. Formation and annihilation of the metastable boron-oxygen complex are found to be thermally activated processes, characterized by two strongly differing activation energies. Intensity-dependent measurements of the defect generation rate show that the defect generation rate increases proportionally with light intensity below 0.01 suns and saturates at higher intensities. All experimental results can be consistently explained by our recently proposed defect reaction model. In this model, fast-diffusing oxygen dimers (O/sub 2i/) are captured by substitutional boron (B/sub s/) to form a metastable B/sub s/-O/sub 2i/ complex. Based on this model, new strategies for an effective reduction of the light degradation in Cz-Si solar cells are derived. Furthermore, the model explains why no lifetime degradation is observed in Al-, Ga- and In-doped Cz-Si materials.