Conduction band offset engineering in wide-bandgap Ag(In,Ga)Se₂solar cells by hybrid buffer layer

Abstract

Ag(In,Ga)Se 2 (AIGS) is one of the promising candidates for the top cell absorber in the tandem structure. However, the conversion efficiency of AIGS solar cells is still lower than that required for the top cell. In this study, to improve the conversion efficiency of AIGS solar cells, we controlled the conduction band offset (CBO) at the buffer layer/ZnO and buffer layer/AIGS interfaces. The reduction in interface recombination at the CdS buffer layer/AIGS interface was achieved by introducing a ZnS(O,OH) buffer layer instead of a CdS buffer layer, although the fill factor (FF ) decreased markedly because the CBO at the ZnS(O,OH)/ZnO interface prevented the electron flow under a forward bias. We found that the introduction of a CdS/ZnS(O,OH) hybrid buffer layer is efficient in controlling the CBO at both the buffer layer/AIGS and buffer layer/ZnO interfaces and improving the solar cell conversion efficiency.

Wide‐gap (Ag,Cu)(In,Ga)Se2 solar cells with different buffer materials—A path to a better heterojunction

“…Later, in 2009, an efficiency of 13.0% ( V OC = 890 mV) was achieved by using an ACIGS absorber with E g = 1.60 eV ([Ag]/([Ag] + [Cu]) ≡ Ag/I = 0.75 and GGI = 0.8) . Recently, in 2017, an efficiency of 9.4% and V OC = 960 V was reached for AIGS with E g = 1.75 eV by using a ZnS(O,OH)/CdS hybrid buffer …”

“…19 Recently, in 2017, an efficiency of 9.4% and V OC = 960 V was reached for AIGS with E g = 1.75 eV by using a ZnS(O,OH)/CdS hybrid buffer. 25 Several changes in material properties are reported when adding…”

Performance Limitations of Wide‐Gap (Ag,Cu)(In,Ga)Se2 Thin‐Film Solar Cells

“…[24] Consequently, some promising V OC values (890-960 mV) could be achieved for ACIGS solar cells with E g ¼ 1.60-1.75 eV and [Ag]/([Ag]þ[Cu]) (AAC) ratios ≥ 0.75. [25][26][27][28] In previous studies, a substantial formation of OVCs was found for group-I (I)-deficient ACIGS within the compositional window of GGI > 0.5 and AAC > 0.5. [29,30] Further investigations revealed that these OVCs are present in the form of isolated patches located at the interfaces, as a consequence of the applied three-stage deposition process.…”

On the Paramount Role of Absorber Stoichiometry in (Ag,Cu)(In,Ga)Se2 Wide‐Gap Solar Cells

“…[ 2 ] Several promising results, with V OC values of 890 mV ≤ V OC ≤ 960 mV and efficiencies of 13% ≥ η ≥ 9.3%, were reported for A(C)IGS solar cells with 1.6 eV ≤ E G ≤ 1.75 eV. [ 20–22 ] However, these efficiencies are still too low to consider wide‐gap ACIGS as a practical top cell absorber material.…”