Exploring dark current voltage characteristics of micromorph silicon tandem cells with computer simulations

Abstract

The transport mechanisms controlling the forward dark current-voltage characteristic of the silicon micromorph tandem solar cell were investigated with numerical modeling techniques. The dark current-voltage characteristics of the micromorph tandem structure at forward voltages show three regions: two with an exponential dependence and a third where the current grows more slowly with the applied voltage. In the first exponential region the current is entirely controlled by recombination through gap states of the top cell. In the second exponential region the current is controlled by the mixture of recombination through gap states of both the top and bottom cells and by free carrier diffusion along the a-Si: H intrinsic layer. In the third region the onset of the electron space charge limited current on the a-Si: H top cell can be observed along with some other mechanisms that are discussed in the paper. The high forward dark J-V curve of the tandem cell can be used as diagnosis tool to quickly inspect the efficiency of the recombination junction in recombining the electron-hole pairs generated under illumination in the top and bottom cells. The dark current at high forward voltages is highly influenced by the amount of electron-hole pairs thermally generated inside the recombination junction.

Factors limiting the open-circuit voltage in microcrystalline silicon solar cells

“…The comparison is shown in Table 2 in brackets with asterisks. We note that the values of references [24,25] are quite close to what we have assumed for our μc-Si:H:F I-layer. In particular the effective DOS in the valence and conduction bands; as well as the tail prefactors G D0 , G A0 are similar to ours and an order of magnitude lower than those normally assumed for hydrogenated amorphous silicon and also assumed for the low (A) and intermediate (B) F c μc-Si:H I-layers here, for reasons to be justified in Section 6.…”

“…Only the capture cross-sections of the dangling bond states are more than two orders of magnitude higher than our case. Probably this had to be assumed for the HWCVD μc-Si I-layers [24,25] since the current density from these devices (13−16 mA cm −2 −22) is much lower than ours (23.20 mA cm −2 ) for comparable values of the absorption coefficients. On the other hand, our average mid gap defect density is the same and their capture cross-sections in the highest F c μc-Si:H I-layer are much closer to the values extracted from modeling the dark J-V characteristics of PECVD μc-Si I layers in reference [22].…”

“…2) to some other modeling results in the literature. Strengers et al [24] and Sturiale et al [25] have modeled the dark and illuminated J-V characteristics of μc-Si solar cells, where the intrinsic layer is deposited by the hot wire CVD (HWCVD) technique. They have observed [24] that in these samples the optical absorption in the red region is much higher than in amorphous silicon.…”

High Efficiency Inorganic/Inorganic Amorphous Silicon/Heterojunction Silicon Tandem Solar Cells

“…Among the tandem PV devices proposed, c-Si-based tandem PV devices have attracted considerable research interests due to their low cost, top sub-cells with tunable optoelectronic properties, and a possible efficiency of as high as 33% in a bifacial configuration 2,3 . To achieve high performance in these tandem solar cells, providing an excellent tunneling-recombination-junction is one of the most important design criteria 4–6 . Another key criterion involves the appropriate choice of top and bottom sub-cells, so that current matching among these sub-cells exists with the same short-circuit current density (J sc ) 5 .…”

Enhanced recovery of light-induced degradation on the micromorph solar cells by electric field

“…12,13 If the leakage paths in top cell can be eliminated and the optimized tunneling recombination junction (TRJ) layer is adopted, higher V oc can be obtained. 14,15 The initial efficiency of the single-junction a-Si cells used in this work was around 9.8% with a V oc of 0.91 V, a J sc of 14.7 mA/cm 2 , and a FF of 74%. For all experiments in this work, the light-induced degradation was stabilized after at least 5 days at AM1.5 exposure under the open-circuit condition.…”