Electrochemical Atomic Layer Growth of a n-p Junction

Monday, 2 October 2017: 12:00
Chesapeake H (Gaylord National Resort and Convention Center)
M. Innocenti (Department of Chemistry - University of Florence, CNR-ICCOM), A. Giaccherini, A. Guerri, M. Vizza (Department of chemistry - University of Florence), E. Berretti (Department of Chemistry - University of Florence), A. Lavacchi (CNR-ICCOM), M. Passaponti (Department of chemistry - University of Florence), S. Caporali (Department of engineering - University of Florence), and F. Di Benedetto (Department of earth sciences - University of Florence)
The increasing in worldwide energy consumption, moved the interest of governments and scientist towards research on renewable energy. Among all the renewables, photovoltaic energy (PV) is one of the most researched technology, because of the availability of its primary energy source (the sun) and the possibility of a direct conversion of solar energy into electric energy. However, the growth of a p-n junction involving non-abundant elements (e.g. CIGS), could have an important drawback in its full life cycle assessment when considering the shortage of the elements and the energy required to assemble the device. Electrodeposition is known for its low energy requirements and facile growth of thin-films of semiconducting materials. In this context, compounds such as Kesterites (CZTS, ternary and quaternary copper and zinc sulfides) could be used in virtue of their semiconducting behavior in conjunction with electrodeposition from aqueous media methodologies to overcome the energy and materials constraints impairing the full exploitation of the actual generation of semiconducting devices. It is important to stress that for the conversion of solar energy in electric energy the charge separation and the bending of the electronic bands occurring at a p-n junction is necessary. Moreover, enhanced transport proprieties (e.g. low concentration of defect) ensure a slow recombination kinetics leading to higher current. Hence, a high quality growth of the p-n junction is crucial to maximize the efficiency and power density of a photovoltaic device. In this context, E-ALD (Electrochemical Atomic Layer Deposition) proven to very suitable for the growth of ordered (even pseudo single crystal) ultra-thin films. Thus, such method seems a legitimate alternative to the high pressure and temperature methods used since today. In recent years we tried to make a proof of concept for the E-ALD growth of a p-n junction. To confirm this proof of concept, in this communication we explore the feasibility of the E-ALD growth for an n-p composite ultra-thin film composed by 60 cycle of Cu2S (p semiconductor and Kesterite precursor) on top of 60 cycle of CdS (with n electronic proprieties). Preliminary electrochemical studies revealed the complex nature of this composite ultra-thin film, impairing the anodic stripping of metals due to a stabilization of the CdS substrate. However, the stability of the substrate and the voltammetric study of a Cu solution in ammonia buffer pointed to the surface limited nature of the Cu deposition step. In order to confirm that the Cu electrodeposition is surface limited several electrochemical and spectroscopical measurements on a composite ultra-thin film Cu2S(60cycle)/CdS(60cycle)/Ag(111) are reported, leading to the confirmation of the layered (p-n) structure of the thin film.