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Tunnel diode current density as a function of voltage. Along path , is controlled by charge carrier tunneling through a very narrow space charge region of the tunnel junction. At point , tunneling ceases to dominate electron transport. Region between the peak and valley current densities is one of negative differential resistance. In region , thermal diffusion through the junction dominates. When integrated within a multijunction solar cell, the tunnel diode experiences a transition in electron transport mode when the cell’s current density exceeds . Arrow indicates the transition when cell performance is traced from open- to short-circuit. Arrow designates the reverse transition when the cell’s curve is traced from short- to open-circuit.
(a) Schematic of localized irradiation tests using a solar fiber-optic minidish concentrator (Ref. 13). (b) (Color online) Photograph (prior to irradiation) with a 1.0-mm-diameter optical fiber placed on the surface of a commercial triple-junction solar cell.
(a) Measured photovoltaic curve, and the corresponding power-voltage curve, characteristic of high-efficiency performance, when . Tracing from open- to short-circuit, or vice versa, yielded identical results (subscripts sc and oc denote short-circuit and open-circuit, respectively). Note that the cell’s voltage is not the same as the tunnel diode voltage in Fig. 1. (b) Cell efficiency as a function of local optical concentration. Data points below the 3200 sun threshold are independent of trace direction.
(a) Measured photovoltaic curves when . Hysteresis is evident from the striking difference depending on whether the curve is traced from open- to short-circuit (solid circles, open arrows) or vice versa (open circles, solid arrows). Points ,,, correspond to those depicted in Fig. 1. (b) Corresponding power-voltage plot, which highlights the difference in maximum power depending on the direction in which cell performance is traced.
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