Best Performance of n+ - p Crystalline Silicon Junction Solar Cells at 300 K, Due to the Effects of Heavy Doping and Impurity Size. I

Abstract

The effects of heavy doping and donor (acceptor) size on the hole (electron)-minority saturation current density JEo(JBo), injected respectively into the heavily (lightly) doped crystalline silicon (Si) emitter (base) region of n+ - p junction, which can be applied to determine the performance of solar cells, being strongly affected by the dark saturation current density: Jo≡JEo + JBo, were investigated. For that, we used an effective Gaussian donor-density profile to determine JEo, and an empirical method of two points to investigate the ideality factor n, short circuit current density Jsc, fill factor (FF), and photovoltaic conversion efficiency η, expressed as functions of the open circuit voltage Voc, giving rise to a satisfactory description of our obtained results, being compared also with other existing theoretical-and-experimental ones. So, in the completely transparent and heavily doped (P-Si) emitter region, CTHD(P-Si)ER, our obtained JEo-results were accurate within 1.78%. This accurate expression for JEo is thus imperative for continuing the performance improvement of solar cell systems. For example, in the physical conditions (PCs) of CTHD (P-Si) ER and of lightly doped (B-Si) base region, LD(B-Si)BR, we obtained the precisions of the order of 8.1% for Jsc, 7.1% for FF, and 5% for η, suggesting thus an accuracy of JBo (≤ 8.1%). Further, in the PCs of completely opaque and heavily doped (S-Si) emitter region, COHD(S-Si)ER, and of lightly doped (acceptor-Si) base region, LD(acceptor-Si)BR, our limiting η-results are equal to: 27.77%,…, 31.55%, according to the Egi-values equal to: 1.12eV ,…, 1.34eV, given in various (B,…, Tl)-Si base regions, respectively, being due to the acceptor-size effect. Furthermore, in the PCs of CTHD (donor-Si) ER and of LD(Tl-Si)BR, our maximal η-values are equal to: 24.28%,…, 31.51%, according to the Egi-values equal to: 1.11eV ,…, 1.70eV, given in various (Sb,…, S)-Si emitter regions, respectively, being due to the donor-size effect. It should be noted that these obtained highest η-values are found to be almost equal, as: 31.51%%≃31.55%, coming from the fact that the two obtained limiting J_o-values are almost the same.