Cu(InGa)Se2 Thin-film Solar Cells with High Resistivity ZnO Buffer Layers Deposited by Atomic Layer Deposition

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Abstract
The aim of our experiments is to improve the performance of Cd-free ZnO/Cu(InGa)Se2 solar cells using a high-resistivity ZnO buffer layer. Buffer layers were deposited by atomic layer deposition (ALD) using diethylzinc (DEZn) and H2O as reactant gases. The structural and electrical properties of the ZnO films on glass substrates were characterized. A high resistivity of more than 103 Ω·cm and a transmittance of above 80% in the visible range were obtained. We focused on determining the optimum deposition parameters for the ALD-ZnO buffer layer. Results indicate that the thickness and resistivity of the ALD-ZnO buffer layer, as well as the heat treatment prior to the deposition of the buffer layer, affect the device characteristics. The best efficiency obtained with an ALD-ZnO buffer layer of solar cells without an antireflective coating was 12.1%. The reversible light soaking effect was observed in these devices.