Grain-boundary recombination in Cu(In,Ga)Se2 solar cells

Abstract

Two-dimensional simulations are performed to investigate the impact of grain boundaries ͑GBs͒ on Cu͑In, Ga͒Se 2 ͑CIGS͒ solar-cell performance. Charged defect levels and compositional variations at GBs are considered. Neutral grain boundaries in the CIGS layer are predicted to be most detrimental if they are parallel to the main junction and located within the depletion region. For columnar GBs with a grain size near 1 m, the effective grain-boundary recombination velocity must be less than 10 4 cm/ s to allow for record-efficiency devices. The majority-hole repulsion ͑additional donors at the GB͒ and the resulting band bending have a small effect on current collection but substantially lower the open-circuit voltage, and the combined effect is generally a lowering of the solar-cell efficiency. Minority-electron repulsion ͑additional acceptors at the GB͒ will partially mitigate GB recombination. A downshift of the valence-band energy, as predicted by the observed Cu depletion at CIGS GBs, can effectively block holes from the GB region and allow efficiencies comparable to GB-free material.

The Effect of Sulfurization Temperature on CuIn(Se,S)2Solar Cells Synthesized by Electrodeposition

“…Consequently, a large number of charge carrier recombination centers are created, which causes significant reduction in the conversion efficiency of the resulting solar cells. 25 The external quantum efficiencies (EQEs) of the devices with the best conversion efficiencies are shown in Figure 4a. The EQE of the CuIn(Se,S) 2 -based solar cell sulfurized at 500…”

Numerical simulation of carrier collection and recombination at grain boundaries in Cu(In,Ga)Se2 solar cells

“…Up until this point, our results are consistent with earlier work. [22][23][24] Here, we also show that the width of the region with lowered valence band energy must be larger than 3 nm, otherwise quantum-mechanical tunneling reduces the passivation effect. If the GB is parallel to the cell surface, the high barriers represent an obstacle for hole transport that strongly reduce the device efficiency.…”

Direct Insight into Grain Boundary Reconstruction in PolycrystallineCu(In,Ga)Se2with Atomic Resolution

“…In particular, for large band bending such that the GBs become type-inverted, i.e., that the electrons become majority carriers, the recombination at GBs may be significantly reduced. Two-dimensional device modeling [5][6][7] showed, however, that such a bend bending at the GBs leads to a reduction in the open-circuit voltage and is thus not beneficial to the overall device efficiency.…”