Explanation for the dark I–V curve of III–V concentrator solar cells

Abstract

The measurement of the dark I-V curve is one of the most straightforward methods for characterizing solar cells. Consequently, an accurate knowledge of its meaning is of high relevance for the comprehension and technological feedback of these devices. In this paper, an explanation of the dark I-V curve for concentrator III-V solar cells is presented using a 3D (three-dimensional) model in order to provide a proper data fit that provides meaningful physical parameters that are also compatible and coherent with a data fit from illumination curves. The influence on the dark I-V curve of the most significant series resistance components of concentrator solar cells is also analysed concluding that only the vertical component as well as the front contact-specific resistance can be assessable by means of this characterization method while both emitter and metal sheet resistances cannot be detected. For comparison purposes, the same experimental data have been fitted by means of a traditional two-diode model showing that, although an accurate dark I-V curve fitting can be achieved, the extracted parameters are unable to reproduce illumination data since lumped models assume the same ohmic losses distribution for both dark and illumination conditions.

Degradation mechanism analysis in temperature stress tests on III–V ultra-high concentrator solar cells using a 3D distributed model

“…Two sets of 18 solar cells were placed inside climatic chambers at different temperatures of 130 and 150 °C. Because the solar cells inside the climatic chambers were in darkness, the current mainly flowed vertically beneath the busbar [13]. The area of the busbar was 0.64 mm 2 .…”

“…This work identifies the failure mechanism in an accelerated temperature stress test carried out on GaAs solar cells in order to improve the quality of these devices. The aim of this work was to analyze the failure mechanism of this kind of solar cell using a 3D distributed model based on elemental circuit units [13]. In this article, we show the potential of the 3D distributed model in the evaluation of degradation in III-V solar cells.…”

“…In the I-V curve, the lateral resistances such as the emitter sheet resistance (r E ), the base sheet resistance (r B ) and the metal sheet resistance (r M ) have a negligible impact on the curve because the current mainly flows vertically beneath the busbar [13]. On the other hand, both the vertical resistance (r v ) and the front grid specific contact resistance (r FC ) show a large influence under dark conditions (see Fig.…”

“…The philosophy of the 3D distributed model has been explained in detail elsewhere [13]. This approach divides the solar cell into elementary units and assigns each unit to a suitable circuit model, depending on its geometry and position in the solar cell: illumination, dark and perimeter ( Figs.…”

Novel accelerated testing method for III–V concentrator solar cells

“…The current density of concentrator solar cells under illumination circulates through the whole active area. However, in this test, forward biasing the cells, the current circulates mainly vertically beneath the bus bar of the solar cell perimeter [12]. The current density has been calculated for the active area in nominal working conditions, and this value, taking the bus bar area into account, is the one used to forward bias the cells in this test.…”