Excess reverse current modeling of single junction Si solar cells and transistor n+pn+ structure effect

In this paper a mechanisms affecting excess reverse currents of silicon single-crystalline solar cells was investigated. In principle, significant reverse currents pertinent to solar cells local and/or global imperfections indicate worse reliability. We carried out experiments of U-I curve measurements of local defect-free samples at different temperatures. Two equivalent circuit models for relatively low and high reverse current range were put forward. The former model indicates initial influence of saturation current and leakage current with resistive character. But, the later model deals with parasitic pn junction near the back contact electrode of solar cell. It turns out that, not fully suppressed junction creates in solar cell n⁺pn⁺ transistor structure and samples behaviour is affected significantly. Least but not least, the full model validity is verified by means of U-I curve approximation of some different samples.