Dynamic Speciation Modeling to Guide Selection of Complexing Agents for Chemical Bath Deposition: Case Study for ZnS Thin Films

Abstract

The dynamic behavior of complexing agents often governs kinetics of chemical bath deposition (CBD), but dynamics are frequently overlooked in favor of a more simplified description of only initial conditions.Here we demonstrate the importance of complexing agent dynamics using a combination of equilibrium speciation modeling and experiments for the case of ZnS thin films grown with three common complexing agents: ethylenediaminetetraacetate (EDTA), nitrilotriacetate (NTA), and citrate, using a reference recipe that ensured fair comparison. Complexing agents control the deposition rate by limiting the availability of free cations. Speciation modeling was used to simulate the free Zn 2+ concentration as a function of total Zn 2+ for baths with the individual agents. Based on the primary stability constants, deposition rate was predicted to decrease abruptly with reaction time for the EDTA bath, whereas baths with NTA or citrate should provide deposition rates that decrease only slightly over time. The predicted deposition profiles of the three baths were observed experimentally using a continuous-flow microreactor for CBD and were supported by the measured total Zn 2+ concentration profiles. Understanding and predicting the dynamic behavior of complexing agents by simulation enables strategic design of CBD processes for many material systems.

Fundamental Aspects and Comprehensive Review on Physical Properties of Chemically Grown Tin-Based Binary Sulfides

“…The preparation of Sn x S y thin films by CBD occurs when a substrate is immersed in the solution mixture of Sn ion (Sn 2+ or Sn 4+ )-source, S ion (S 2− )-source, and an appropriate complexing agent. In the deposition process, the Sn 2+ /Sn 4+ ions are complexed through the coordinated bond formation by the complexing agent, which controls the rate of reaction [ 148 ]. At super saturation condition (Ionic product, Q ip > Solubility product K sp ), Sn x S y films can be deposited ( Figure 5 c).…”

“…Therefore, it is vital to monitor supersaturation with respect to an individual phase as well as the growth kinetics. In addition, the K sp of Sn x S y is affected by the concentration of precursor, solvent type, bath temperature, and bath pH [ 148 , 149 ]. Therefore, the optimum condition for the deposition of Sn x S y thin film can be achieved by manipulating the above deposition parameters.…”

Impact of Annealing Thin Films In(OH)xSy Growth By Solution Technique

“…The optical band gap value reported for indium sulphide thin films lies in range 2.0-2.4 eV depending on the physical or chemical process deposition [2]. One possibility to induce anomalous broadening of the optical band gap is to substitute some sulphur with oxygen in order to synthesize a homogeneous In2S3-3xO3x [14]. Another possibility of a buffer containing hydroxides or oxides and hydroxides is by use of CBD for sulphides, since the composition of a buffer layer often depends on the deposition method and the preparation condition [9].…”

“…According to the research done on the electronic engineering of solid-state DSSC, passivation of interface recombination can be of fundamental importance in systems like ETAsolar cells [6] and In(OH)xSy is one of the proposed buffer layers [18]. The In(OH)xSy layers have been deposited by a wet CBD and has proved to be a good buffer for TiO2 solar cells with its band gap energy varying in the range 2.4-3.4 eV depending on stoichiometry of In(OH)xSy [14,24]. The dark I-V characteristics obtained confirm that In(OH)xSy coating was good and free of pin holes that can lead to shorting of the current.…”

Nanocrystalline and monophasic thin films of metal chalcogenide (FeS, ZnS) and oxide (ZnO) by chemical bath deposition (CBD)

“…Deposition of uniform ZnS thin films by CBD is a bit tricky compared to the deposition of CdS and ZnO by the same technique, owing to the chemistry of reactions taking place to produce ZnS thin films by CBD. The role of complexing agent along with pH of the solution has crucial importance in deposition of oxygen free ZnS thin films by CBD . Optimized conditions for the growth of nanocrystalline ZnS thin films by CBD have been reported recently by the authors .…”