Locating the electrical junctions in Cu(In,Ga)Se₂ and Cu₂ZnSnSe₄ solar cells by scanning capacitance spectroscopy

Abstract

We determined the electrical junction (EJ) locations in Cu(In,Ga)Se 2 (CIGS) and Cu 2 ZnSnSe 4 (CZTS) solar cells with 20-nm accuracy by developing scanning capacitance spectroscopy (SCS) applicable to the thin-film devices. Crosssectional sample preparation for the SCS measurement was developed by high-energy ion milling at room temperature for polishing the cross section to make it flat, followed by low-energy ion milling at liquid nitrogen temperature for removing the damaged layer and subsequent annealing for growing a native oxide layer. The SCS shows distinct p-type, transitional, and n-type spectra across the devices, and the spectral features change rapidly with location in the depletion region, which results in determining the EJ with~20-nm resolution. We found an n-type CIGS in the region next to the CIGS/CdS interface; thus, the cell is a homojunction. The EJ is~40 nm from the interface on the CIGS side. In contrast, such an n-type CZTS was not found in the CZTS/CdS cells. The EJ is~20 nm from the CZTS/CdS interface, which is consistent with asymmetrical carrier concentrations of the p-CZTS and n-CdS in a heterojunction cell. Our results of unambiguously determination of the junction locations contribute significantly to understanding the large open-circuit voltage difference between CIGS and CZTS.

N‐Type Surface Design for p‐Type CZTSSe Thin Film to Attain High Efficiency

“…inversion, an excellent strategy to promote the efficiency of CIGSSe solar cells greatly, [20,21] is still a huge challenge for the kesterite solar cell.…”

“…[ 14,18 ] Theoretical calculations and experimental results both show that Ag 2 ZnSn(S,Se) 4 is an n‐type material and can form a p–n junction with CZTSSe, [ 13,15,19 ] but it cannot ensure the existence of n‐type (Cu,Ag) 2 ZnSn(S,Se) 4 on the surface due to the quick diffusion of Ag. So far, surface type inversion, an excellent strategy to promote the efficiency of CIGSSe solar cells greatly, [ 20,21 ] is still a huge challenge for the kesterite solar cell.…”

Delafossite CuAlO2 Modification‐Induced Synergistic Passivation Effects for Heterojunction Interface and Absorber toward Efficient Kesterite Solar Cells

“…Yet, the above HEI field passivation effect belongs to the heterogeneous field passivation (HEFP) similar to the cases of back electrode interface (BEI) optimization, [36,37] which commonly needs an extra preparation process and also may encounter lattice mismatch issue as compared to the homogeneous field passivation (HOFP) in CIGSSe solar cells. [33,38] In addition, it is worthwhile to note that no systematic researches regarding the combination of HEI passivation and absorber optimization have been currently reported. Thus, a new passivation strategy aiming for the synergistic passivation effects (SPE) for HEIs and absorbers remains to be explored apart from the reported passivation works referring to BEIs and absorbers, [39,40] especially for the simultaneous realization of HOFP construction at HEI and bulk GB passivation.…”