The causes of the degradation of electrical characteristics of solar cells were evaluated by using a small p–n diode array fabricated on a multi-crystalline silicon substrate. It was found that many of the current–voltage characteristics of diodes with grain boundaries deteriorated, but some deteriorated diodes without grain boundaries were also found. Electron beam-induced current imaging, photoluminescence mapping, transmission electron microscopy and electron back-scatter diffractometry were used to determine the causes of degradation. It was concluded that the electrical characteristics were severely deteriorated by the existence of small-angle grain boundaries. Multi-crystalline silicon solar-cell efficiency was significantly affected not only by obvious grain boundaries but also by small-angle grain boundaries which consisted of periodically aligned dislocations and perhaps metallic and oxygen impurities.

Study of the Degradation of p–n Diode Characteristics Caused by Small-Angle Grain Boundaries in Multi-Crystalline Silicon Substrate for Solar Cells. T.Tachibana, J.Masuda, K.Imai, A.Ogura, Y.Ohshita, K.Arafune, M.Tajima: Japanese Journal of Applied Physics, 2009, 48[12], 121202