Takahito Nishimura

1 Introduction Transparent-conductive-oxide (TCO) thin films have gained prominence in various application fields such as solar cells,[1, 2] light-emitting diodes,[3] and gas sensors.[4] The most widely recognized TCO thin films, such as In2O3[5, 6] and ZnO,[7, 8] are typically n-type semiconductors. While these n-type TCO materials have been extensively researched and adopted, p-type TCO has not been studied as much as n-type TCO.

1 Introduction The n-type buffer layer in thin-film solar cells is essential for achieving high efficiency. Traditionally, cadmium sulfide (CdS) deposited via chemical bath deposition (CBD) is used for this purpose. However, CBD inevitably results in the formation of colloids, which degrade the solution and incur significant costs for waste solution disposal. In addition, CdS contains cadmium, which poses environmental concerns.

1 Introduction The n-type buffer layer considerably affects the conversion efficiency of thin-film solar cells.