Influence of Ligands on the Formation of Kesterite Thin Films for Solar Cells: A Comparative Study

Abstract

The preparation of solar-cell-grade Cu2 ZnSnS4 (CZTS) thin films from ligand-capped small-grained CZTS particles remains hindered by problems of phase segregation, composition non-uniformity, and in particular carbon-layer formation. Herein, through a systematic comparative study of annealed films of CZTS nanocrystals prepared using conventional oleylamine and those prepared using formamide, these problems are found to be mainly attributable to the influence of the ligands, and mechanisms are proposed. Importantly, the origin of the carbon layer in oleylamine-capped CZTS films is revealed to be the reaction between oleylamine and sulfur. This carbon layer has a very poor electrical conductivity, which can be the reason for the limited performance of such films. Fortunately, these problems can almost all be avoided by replacing oleylamine with formamide to form CZTS films.

Enhanced external quantum efficiency from Cu2ZnSn(S,Se)4 solar cells prepared from nanoparticle inks

“…2(c) as no such bottom FG layers are obtained in carbon free techniques. [20][21][22] The small network of grain boundaries in the FG layer may contribute high series resistance and reduce the fill factor of solar cells. 11,23,24) It is difficult to draw conclusions about the total thickness of the entire film due to the combination of uncertainty in the precursor thickness (nominally 1.0 ± 0.1 µm) and surface roughness however, it can be clearly seen that as the thickness of the FG layer increases, the MoSe 2 layer becomes thinner.…”

Direct evidence of causality between chemical purity and band-edge potential fluctuations in nanoparticle ink-based Cu2ZnSn(S,Se)4 solar cells

“…Table S1. CZTS nanoparticles were fabricated using a hot-injection method where a sulphur-OLA solution was injected into a hot metallic precursors-OLA solution (Qu et al, 2014). The resulting nanoparticle inks were deposited on molybdenum substrates via spin coating to form the CZTS precursor thin lm with a thickness around 1 µm (Qu et al, 2016a).…”

Influence of OLA and FA ligands on the optical and electronic properties of Cu2ZnSn(S, Se)4 thin films and solar cells prepared from nanoparticle inks

“…Huang et al recently suggested the use of formamide (FA) instead of OLA to produce single CZTS absorber layer without the FG layer (Huang et al, 2015). Surprisingly, despite a complete comparison of the microstructure properties of the absorber layer (Huang et al, 2016), there is no functional device reported from nanoparticle synthesized with FA. In this paper, we demonstrate working solar cells using a dual ligands approach via a stack of FA and OLA based absorbers: the FA absorber is used to provide a reduced back contact barrier height while the OLA absorber ensures a functioning pn-junction.…”