Saeed Bayat | Searcharxiv

arXiv2026

What enables GaOx as hole transport layer for a 16 percent 1.0 eV CuInSe2 Bottom Cells with VOC above 550 mV?

Among the highly efficient photovoltaic technologies, that do not rely on epitaxy, only chalcopyrites have a bandgap tunable down to 1.00 eV, the ideal for tandem applications. This is obtained with a pure CuInSe2 absorber without Ga. GaOx has been shown to be an efficient hole transport layer that prevents recombination at the metallic back contact. On the other hand, GaOx has proven detrimental, when it forms on In containing transparent back contacts in bifacial solar cells. Here, we investigate the conditions that make the GaOx layer conductive. We employ a GaOx hole transport layer that is formed through ion exchange during co-evaporation of the low band gap absorber layer. We find that no additional Cu is needed, and that Na is not necessary for a conductive GaOx. Nor did we find a systematic influence of oxygen flow during the sputtering process of the oxide layer. The GaOx layer is partly crystalline. The optimized passivating hole transport layer enables a CuInSe2 bottom solar cell, without any addition of Ag or heavy alkalis, with an active area efficiency above 16% and a record-certified open-circuit voltage VOC of 552meV

cond-mat.mtrl-sci↗

arXiv2025

Sub-micron Cu(In,Ga)Se2 solar cell with efficiency of 18.2% enabled by a hole transport layer

Reducing the thickness of Cu(In,Ga)Se2 solar cells is a key objective in order to reduce production cost and to improve sustainability. The major challenge for sub-micron Cu(In,Ga)Se2 cells is the recombination at the backside. In standard Cu(In,Ga)Se2 backside recombination is suppressed by a bandgap gradient, acting as a back surface field. This gradient is difficult to maintain in sub-micron thick absorbers. In this study, a hole transport layer passivates the back contact and enables efficient sub-micron Cu(In,Ga)Se2 solar cells without the need of a Ga gradient. The backside passivation by the hole transport layer is as effective as an optimized Ga gradient, resulting in a significant increase in open-circuit voltage by 80 mV in comparison to the reference sample without passivation. Moreover, the hole transport layer exhibits good transport properties, leading to a fill factor as high as 77%. Photoluminescence quantum yield of 0.15% and solar cell efficiency above 18% are demonstrated in sub-micron Cu(In,Ga)Se2 absorbers.

cond-mat.mtrl-sci↗