Atomic-layer-deposited buffer layers for thin film solar cells using earth-abundant absorber materials: A review

Abstract

Atomic layer deposition (ALD) is not just a thin film deposition technology limited to the semiconductor IC industries to grow high-k gate dielectric or a Cu diffusion barrier layer. In recent times, it has found plenty of applications in the field of renewable energy due to its precise thickness control up to few angstroms and its unique feature of conformal and uniform coating on any randomly shaped 3D structure. ALD has far-reaching applications in this field, including electrochemical storage, fuel cells, solar photovoltaics (PV), and catalysis for water splitting to produce H2 as a green fuel. In solar PV technology, ALD is now being extensively used as an efficient tool to deposit surface passivation layers, absorber or sensitizer, transparent conducting oxide, and barrier and buffer layers in several kinds of solar cells. Out of all the different layers associated with a solar cell, ALD is majorly used for the development of a very thin n-type buffer layer. This review article presents a systematic chronological study on such ALD-grown buffer layers for thin film solar cells (TSFCs). The study is carried out in detail based on different earth-abundant absorber materials, such as Cu2ZnSn(S,Se)4 (CZTSSe), Cu2O and SnS, for which ALD is successfully used to deposit the buffer layer.