Monolithic CZTS-on-Silicon Tandem Solar Cells: Prospects and Challenges

Description

We have systematically investigated the possible detrimental effects of monolithic integration of Cu2ZnSnS4 (CZTS) on a Tunnelling Oxide Passivated Contact (TOPCon) silicon cell, as promising representatives for a cheap, stable and earth abundant tandem solar cell. We have studied the role of TiN, as the barrier layer in between the two absorbers, and discuss the implications on the performance of the tandem device. Measurements of minority carrier lifetime revealed that Cu diffusion from CZTS into silicon is not as severe as diffusion from pure Cu. Moreover, a promising implied Voc (i-Voc) above 700 mV for Si was measured after the high-temperature CZTS synthesis on Si, despite a 40% percent decrease from initial effective lifetime. Further investigations are required to understand the role of TiN as the barrier layer, because even though the decrease in lifetime seems to be independent of TiN thickness, Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) measurements show an effective blocking of diffusing species, when TiN is present as a barrier layer. Further SIMS and Deep-level Transient Spectroscopy (DLTS) characterizations on silicon, where both TiN and CZTS are removed, are planned for more precise measurement of trace elements. Ultimately, asymmetrically passivated TOPCon device wafers with i-Voc above 710 mV were prepared for the fabrication of monolithic tandem devices with different barrier configurations.

Period	8 Apr 2019
Held at	SiliconPV 2019
Event type	Conference
Location	Leuven, Belgium
Degree of Recognition	International