Relating Deposition Conditions to Zn(S,O,OH) Thin Film Properties for Photovoltaic Buffer Layers Using a Continuous Flow Microreactor

Opasanont, Borirak; Kuba, Austin G.; Louderback, Evan G.; Choudhury, Kaushik Roy; Baxter, Jason B.

doi:10.1021/cm501642a

Cited by 11 publications

(20 citation statements)

References 42 publications

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“…In alkaline Zn(S,O,OH) deposition, oxygen inclusion can yield S/ (S + O) atomic ratios as low as 0.42. 11 Deposition at lower pH should yield less oxygen since the ZnO and Zn(OH) 2 phases are undersaturated versus their solubility products, but deposition rates are slow. Here, deposition was performed under near-neutral pH conditions because they provide sufficiently fast reaction rates with the thioacetamide (TAA) sulfur source and potentially reduce oxygen inclusion.…”

Section: ■ Introductionmentioning

confidence: 99%

Adherent and Conformal Zn(S,O,OH) Thin Films by Rapid Chemical Bath Deposition with Hexamethylenetetramine Additive

Opasanont

Van

Kuba

et al. 2015

ACS Appl. Mater. Interfaces

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ZnS is a wide band gap semiconductor whose many applications, such as photovoltaic buffer layers, require uniform and continuous films down to several nanometers thick. Chemical bath deposition (CBD) is a simple, low-cost, and scalable technique to deposit such inorganic films. However, previous attempts at CBD of ZnS have often resulted in nodular noncontinuous films, slow growth rates at low pH, and high ratio of oxygen impurities at high pH. In this work, ZnS thin films were grown by adding hexamethylenetetramine (HMTA) to a conventional recipe that uses zinc sulfate, nitrilotriacetic acid trisodium salt, and thioacetamide. Dynamic bath characterization showed that HMTA helps the bath to maintain near-neutral pH and also acts as a catalyst, which leads to fast nucleation and deposition rates, continuous films, and less oxygen impurities in the films. Films deposited on glass from HMTA-containing bath were uniform, continuous, and 90 nm thick after 1 h, as opposed to films grown without HMTA that were ∼3 times thinner and more nodular. On Cu2(Zn,Sn)Se4, films grown with HMTA were continuous within 10 min. The films have comparatively few oxygen impurities, with S/(S+O) atomic ratio of 88%, and high optical transmission of 98% at 360 nm. The Zn(S,O,OH) films exhibit excellent adhesion to glass and high resistivity, which make them ideal nucleation layers for other metal sulfides. Their promise as a nucleation layer was demonstrated with the deposition of thin, continuous Sb2S3 overlayers. This novel HMTA chemistry enables rapid deposition of Zn(S,O,OH) thin films to serve as a nucleation layer, a photovoltaic buffer layer, or an extremely thin continuous coating for thin film applications. HMTA may also be applied in a similar manner for solution deposition of other metal chalcogenide and oxide thin films with superior properties.

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Section: ■ Introductionmentioning

confidence: 99%

Adherent and Conformal Zn(S,O,OH) Thin Films by Rapid Chemical Bath Deposition with Hexamethylenetetramine Additive

Opasanont

Van

Kuba

et al. 2015

ACS Appl. Mater. Interfaces

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“…In our previous works, we experimentally measured the time-resolved concentration of S 2-ion in the bath for a more accurate determination of deposition driving forces by this pathway. [18][19][20] In this work, we compare the behavior of complexing agents by using a reference recipe that we recently developed for rapid deposition of low-oxygen ZnS films for photovoltaic buffer layer and nucleation layer applications. 20 The near-neutral chemistry has a different dominant deposition pathway than the typical ion reaction as described above, but the conclusions can be extended to any system that ions, 23 and thus does not complicate the modeling of speciation.…”

Section: Introductionmentioning

confidence: 99%

“…Second, HCl was used for adjustment of starting pH instead of H2SO4. Cl -binds very weakly to Zn 2+ because of the low primary Ks value(Table 1), and hence the free Zn 2+ concentration will not be significantly affected by the different amounts of HCl needed for different complexing agents.In the microreactor film deposition, the microreactor reported in ref 19 was used 19. Two syringe pumps fed the precursor solutions through a dynamic mixer to the microreactor inlet.…”

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

Opasanont

Baxter

2015

Crystal Growth & Design

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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.

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“…While many different groups have reported using them to make liquid and gas products including dyes and pharmaceuticals, (Kiwi-Minsker and Renken, 2005;Haswell, 2005, 2003;Watts and Wiles, 2007;Wille et al, 2004) microreactors have only recently been used to deposit solid materials on surfaces. (Opasanont et al, 2014;McPeak et al, 2013;Chang et al, 2009;Choi et al, 2013;Jung et al, 2008;Mugdur et al, 2007;Su et al, 2013). Recently there has been a report of combining the two concepts and using EPD to deposit metal nanoparticles in a flow reactor.…”

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Thin films of copper indium selenide fabricated with high atom economy by electrophoretic deposition of nanocrystals under flow

Dillon

Göktaş

et al. 2016

Chemical Engineering Science

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Electrophoretic deposition (EPD) of colloidal nanocrystals (NCs) under flow is explored as a general method for the fabrication of semiconducting thin films. For photovoltaic applications, a low process voltage is highly desirable to avoid damaging the accreting semiconductor. Here we report a continuous flow reactor design that can operate at reduced voltage compared to a traditional batch reactor while preserving the electrophoretic velocity of the NCs by utilizing narrow electrode spacing. In a batch reactor, the low ratio of reactor volume to electrode surface area dictated by such a narrow spacing of the electrodes would impose a limit on the mass of nanocrystals that are resident in the reactor and therefore the thickness of the films that can be deposited.By continuously flowing the colloidal dispersion of NCs this limitation is obviated and thick films can be deposited. Through modeling and experiment we demonstrate the process parameters necessary to completely utilize the NCs in the feed solution, thereby achieving nearly 100% atom economy in the deposition process. The reactor design is 2 compatible with large area substrates and is specifically designed to enable continuous, high-rate fabrication of the active layer of photovoltaic cells.

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Relating Deposition Conditions to Zn(S,O,OH) Thin Film Properties for Photovoltaic Buffer Layers Using a Continuous Flow Microreactor

Cited by 11 publications

References 42 publications

Adherent and Conformal Zn(S,O,OH) Thin Films by Rapid Chemical Bath Deposition with Hexamethylenetetramine Additive

Adherent and Conformal Zn(S,O,OH) Thin Films by Rapid Chemical Bath Deposition with Hexamethylenetetramine Additive

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

Thin films of copper indium selenide fabricated with high atom economy by electrophoretic deposition of nanocrystals under flow

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