Shunt types in crystalline silicon solar cells

Abstract

Nine different types of shunt have been found in state-of-the-art mono-and multicrystalline solar cells by lock-in thermography and identified by SEM investigation (including EBIC), TEM and EDX. These shunts differ by the type of their I-V characteristics (linear or nonlinear) and by their physical origin. Six shunt types are process-induced, and three are caused by grown-in defects of the material. The most important process-induced shunts are residues of the emitter at the edge of the cells, cracks, recombination sites at the cell edge, Schottky-type shunts below grid lines, scratches, and aluminum particles at the surface. The material-induced shunts are strong recombination sites at grown-in defects (e.g., metal-decorated small-angle grain boundaries), grown-in macroscopic Si 3 N 4 inclusions, and inversion layers caused by microscopic SiC precipitates on grain boundaries crossing the wafer.

Understanding junction breakdown in multicrystalline solar cells

“…Ohmic hot spots may also be caused by incomplete edge junction isolation, by cracks, or by grown-in SiC filaments. 1 The defect-induced breakdown type 2 is often the dominating one in the interesting bias range up to À13 V. However, as Figs. 2(b) and 2(e) show, there are usually many of these breakdown sites distributed across the cell area.…”

“…They may be caused by incomplete edge junction isolation, by cracks, by Al contamination of the emitter, or they may be material-induced. 1 In the latter case they are usually due to n-conducting SiC filaments crossing the bulk, which exist preferably in grain boundaries of material from the upper part of the block. 2 The present contribution will not deal with these ohmic shunts but will concentrate on junction breakdown processes under reverse bias.…”

Universality of non-Ohmic shunt leakage in thin-film solar cells

“…For example, we would like to note that this phenomenon of nonOhmic shunt leakage current is not limited to thin-film solar cells, but has also been observed for a variety of solar cells including crystalline silicon. 18 Based on the apparent similarity of this behavior for all these cells, we believe that the proposed model of SCL current could, in principle, be extended to all solar cells in general. Given the general structure of solar cells and their relatively large areas, the possibility of formation of a parasitic shunt path is quite high.…”

“…In this equivalent circuit picture, the shunt current ͑I sh , through the parallel resistance R sh ͒ and the exponential diode current ͑I d ͒ account for the net dark current ͑I dark ͒ However, this picture has been shown to be incomplete since shunt leakage currents are known to exhibit a nonlinear dependence on the applied voltage. 8,9,13,18,19 Some equivalent circuits incorporating a parasitic weak diode have also been proposed to account for these nonlinear shunts. [19][20][21] However, these macroscopic, circuit level models cannot account for the microscopic nature of shunt paths.…”

Shunt removal and patching for crystalline silicon solar cells using infrared imaging and laser cutting

“…The linear shunts are more harmful to cell performance than the nonlinear ones, and all of the linear shunts can be present in the image obtained under reverse bias [13]. So, during the boundary identification process between the shunted and nonshunted regions, all infrared images except that of the initial sample A were taken under reverse bias to exclude the interference of the nonlinear shunts.…”