• Engberg, Sara Lena Josefin
• Crovetto, Andrea
• Hansen, Ole
• Schou, Jørgen

Abstract

We have studied the effect of dopants such as Na, Sb, and Li in Cu2ZnSnS4 nanoparticle thin films [1]. The as-synthesized CZTS nanoparticles were inherently ligand-free [2], which allows the use of polar solvents, such as water and ethanol. Another advantage of these particles is that the user- and environmentally-friendly chloride salts can be directly dissolved in controllable amounts. This further circumvents the need for later incorporation of dopants, or a ligand-exchange step to functionalize the surface of the nanoparticles. In addition, the homogeneous distribution of additives in the ink allows uniform grain growth within the deposited absorber layer. By including Na in the nanoparticle ink, micron-sized grains throughout the whole absorber are achieved after annealing in a sulfur atmosphere at 600°C. The absorber layer appeared to be of full density, and no closed porosity could be detected. In addition, the photoluminescence signal increased by a factor of 200 after Na-inclusion. Without Na, the grains were very difficult to sinter, the film was porous, and the photoluminescence was low.This suggests that including Na reduces interface recombination in CZTS nanoparticle absorber layers. A concentration of Na/(Cu+Zn+Sn)=30% was necessary for the densification of the absorber, which is significantly higher than that used in other Na-doped CZTS systems. The annealed films were found to be of the desired Cu-poor and Zn-rich composition.<br/>

Topics

• nanoparticle
• porous
• density
• impedance spectroscopy
• surface
• photoluminescence
• grain
• inclusion
• thin film
• annealing
• porosity
• densification
• grain growth