The competing roles of i-ZnO in Cu(In,Ga)Se2 solar cells

Abstract

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Cu(In,Ga)Se2 Solar Cells with Amorphous In2O3-Based Front Contact Layers

“…However, it is difficult to synthesize homogeneous junctions free of pinholes and weak diodes when fabricating large-size modules or even in small-size solar cells containing rough CIGS interfaces. In such cases, the insertion of a high-resistive TOS layer was confirmed to be effective in mitigating the drop in produced by local shunts and weak diodes. − Additionally, simulations of solar cells having spatially inhomogeneous electronic properties suggested that the optimum series resistance mitigating the V oc and FF drop was determined by the degree of inhomogeneities. , However, as will be described herein, it is difficult to control the resistivity of unintentionally doped polycrystalline ( poly -) ZnO layers. Conversely, amorphous TOSs ( a -TOSs) comprised of post-transition metal cations with a ( n – 1)­d 10 n s 0 ( n ≥ 4) electronic configuration , are promising high-resistive layer candidates.…”

Optimization of Intrinsic ZnO Thickness in Cu(In,Ga)Se2-Based Thin Film Solar Cells

“…The highly resistive i-ZnO film plays an important role in achieving high-efficiency CIGS solar cells, while working as a shield to protect the CdS/CIGS junction from damage during direct current (DC) sputtering of the highly conductive AZO film [13]. The i-ZnO improves the open-circuit voltage (V OC ) and fill factor (FF) by reducing the shunt paths [14,15,16]. In general, the shunt path could form by the presence of pinholes in the CdS buffer layer causing the direct contact of conductive elements (e.g., Al, Ga, and B) in transparent conductive oxide (TCO) with CIGS absorber (Figure 1a) and the leakage of current through these shunts’ path [14,17].…”

“…The i-ZnO improves the open-circuit voltage (V OC ) and fill factor (FF) by reducing the shunt paths [14,15,16]. In general, the shunt path could form by the presence of pinholes in the CdS buffer layer causing the direct contact of conductive elements (e.g., Al, Ga, and B) in transparent conductive oxide (TCO) with CIGS absorber (Figure 1a) and the leakage of current through these shunts’ path [14,17]. Furthermore, an i-ZnO layer forms cliff-like conduction band alignment with a CdS buffer layer and make the generated electron from the CIGS absorber move to front contact effectively [18].…”

Atomic Layer Deposition of Ultrathin ZnO Films for Hybrid Window Layers for Cu(Inx,Ga1−x)Se2 Solar Cells

“…This i-ZnO window layer effectively blocks the short-circuit pathways through the voids in the CdS buffer layer, and consequently enhances the shunt resistance (R sh ), fill factor (FF), and open-circuit voltage (V OC ) of the solar cells. In addition, the i-ZnO window layer protects the CdS buffer layer during the subsequent deposition of a TCO layer [5][6][7][8].…”

“…To overcome the drawbacks of sputter coating, atomic layer deposition (ALD) processes have been proposed for fabrication of the ZnO window layers in CIGS thin-film solar cells. Although the ALD technique is a well-established deposition method for precise fabrication of ultrathin films [13][14][15], few studies have reported on ALD of ZnO window layers for thin-film chalcogenide solar cells [5,16,17]. Such reports that exist have focused on the material properties of atomic-layer-deposited ZnO (A-ZnO).…”