Growth of Zn‐Ge‐O Thin‐Film as a Transparent Conductive Oxide Buffer Material for Chalcopyrite Solar Cell

Abstract

AbstractThe importance of positive band offset at the p–n interface of heterojunction thin‐film solar cells has been underlined in the authors' previous work on theoretical study of the role of n‐type layer in determining open‐circuit voltage – and experimental work by other research groups. An n‐type material with low electron affinity has the potential to fulfill the requirements for producing a high‐performance heterojunction thin‐film solar cell. In this current work, a new alternative transparent conductive oxide material for chalcopyrite heterojunction solar cells is investigated by alloying ZnO and GeO2 to grow a Zn‐Ge‐O thin‐film with low electron affinity. The film is grown by metal organic chemical vapor deposition with tetramethoxygermanium as the Ge source. Through film characterization, it is confirmed that higher concentrations of Ge in the film result in lower electron affinities and relatively constant valence band maximums. Different [Ge] / ([Zn] + [Ge]) also affects the film morphology, from polycrystalline at a lower concentration of Ge to aggregation of nanocrystals at a higher concentration of Ge. Electronic characterization and preliminary device application test show promising results for the future of the Zn‐Ge‐O thin‐film as an alternative n‐type layer for chalcopyrite solar cells.