Investigation of TiN and TiO2 as barrier layer in Silicon/Chalcogenide Tandem Solar Cells

Description

Silicon-based tandem solar cells are one of the promising approaches to increase the efficiency of photovoltaic devices beyond the single-material detailed-balance limit while benefiting from the well-established technology of the conventional silicon solar cells. However, an inexpensive, earth abundant, stable and non-toxic material with a proper band-gap has not yet been identified for the upper cell. We suggest CZTS, a chalcogenide with a bandgap of 1.5 eV, as a promising material for the top absorber. The presence of a high temperature (500-600 oC) annealing process in a sulfur-rich atmosphere during synthesis of CZTS makes monolithic integration challenging. Thus, a barrier layer is necessary between the two absorbers. This barrier layer must act effectively as a diffusion barrier and allow exchange of charge carriers between the two cells. In this research, we investigated various layers of TiN and TiO2, deposited with (PE)ALD, as potential materials for the barrier layer. For this purpose, simple stacks of Cu/(~25nm)TiN/Si and Cu/(~80nm)TiO2/Si were prepared, and systematic isothermal annealing experiments at 550 oC in vacuum were performed to simulate the CZTS synthesis conditions. Subsequently, the samples were characterized by XRD, XPS, and sheet resistance measurements to evaluate the effectiveness of TiN and TiO2 as diffusion barriers. Furthermore, optical simulations were done to determine the optical performance of these layers in the near infrared spectrum.

Period	19 Jun 2018
Event title	European Materials Research Society: 2018 Spring Meeting
Event type	Conference
Location	Strasbourg, FranceShow on map
Degree of Recognition	International