Post on 12-Apr-2017
hot plate dry300 oC
spin-coat
3000rpm, 30sMo Mo Mo
repeat to obtain desired thickness
Mo
sulfurizationin S vapor
500 oC, 1 hr
Film characterizationsXRD, SEM, EDS
apply ink
Spincoating+sulfurization
Sonication inand wash withEtOH, dispersed in EtOH
Drop-cast+sulfurization
+ EDS resultsCu1.6ZnSnS4Impurities (atom%): N (8%), Cl (1%)XRD available
+ EDS resultsCu1.6ZnSn0.8S2.8Impurities (atom%): N (35%), C (35%)XRD available
Very poor adhesion
Ink 5
Ink DF5
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MethodsInk Type 2: inorganic metal salts and chalcogen sources dispersed in solvents (Example: CuCl, Zn(NO)2, SnCl2, thiourea dispersed in non-toxic solvents)
Advantages: disadvantages:non-toxic solvents reaction by-products
easy to formulate material dispersion
impurities
Adv. Energy Mater., 2011, 1, 732-735
Development of Cu2ZnSnS4 Inks for Solution Processable Thin Film Solar Cells
Feng Jiang and Anthony Muscatmuscat@email.arizona.edu
Department of Chemical and Environmental EngineeringUniversity of Arizona, Tucson, AZ 85721Introduction
Comparing to CuInGaS2 (CIGS), kesterite Cu2ZnSnS4 (CZTS) has been considered as a more ideal absorber material for the next generation low-cost solar cell, due to the lack of rear and expensive indium. With a direct band gap of 1.0-1.5 eV and absorption coefficient larger than 104 cm-1, CZTS based thin film solar cell has reached reported efficiency up to 9.6%. Although vacuum sputtering has been used to deposit CZTS film, it is difficult to control the chemical stoichiometry during the deposition, resulting undesired crystalline phases and impairing the cell efficiency. Solution processable thin film fabrication not only opens the door for precise control of film stoichiometry, but also creates the opportunity for being adapted into large scale, continuous roll-to-roll solar cell manufacturing. This work gives a quick review of three types of major ink formulations for CZTS cells. Then we present our experiment results on one of these formulations, which is based on having inorganic metal salts and chalcogen sources dispersed in common organic solvents. Concentration, pH, and precursor ratio were systematically changed to optimize the ink formulation in order to obtain an adhesive and stoichiometric CZTS film. Review on InksThe requirements of an ink for thin film solar cell fabrication: - contains metal chalcogenides or ready-to-react metal and chalcogen sources - has metal precursors close to the oxidation states of target material - minimizes the impurity contents that is hard to remove - has a good material dispersion (i.e. no severe agglomeration) - uses non-toxic solvents with low boiling points - has an adjustable viscosity that is adaptable to the deposition methods - is easy to formulate and processWhy these requirements - to fabricate a dense film with large grain size and small number of voids: lower impurities in the ink; minimize reactions that impede crystallization; accelerate solvent evaporation - to incorporate the ink into mass production line without extra costs and safety issues
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MethodsInk Type 1: metals and metal chalcogenides dissolved in solvents (Example: Cu2S, Zn, SnSe, S and Se dissolved in N2H4)
Prog. Photovolt: Res. Appl., 2012, 20, 6-11 Adv. Mater. DOI: 10.1002/adma.201201785
Advantages: disadvantages:no carbon content toxic solvent
good material dispersion
no reaction by-product
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Equipments and Preliminary results
Ink Types Major Equipments Preliminary results
Ink type 1 glove box dense, low-voids, large grain CZTS film, cell efficiency 10.1%1
Ink type 2 N/A CZTS film with smaller grains and some voids, cell efficiency 4.1%2
Ink type 3 milling machine, vacuum oven
dense, low-voids, large grain CZTS and CIGS films, cell efficiency exceeds 10%3
1. Prog. Photovolt: Res. Appl., 2012, 20, 6-11 2. Adv. Energy Mater., 2011, 1, 732-7353. Thin Solid Films, 2003, 431-432, 53-57
Back to TOC
Reference:1. Prog. Photovolt: Res. Appl., 2012, 20,
6-11 2. Adv. Energy Mater., 2011, 1, 732-7353. Thin Solid Films, 2003, 431-432, 53-
57
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MethodsInk Type 3: nanoparticles of metal oxides/ chalcogenidesdispersed in solvents (Example: CuO, In2O3, Ga2O3 (for CIGS) and Cu2S, Zn, Sn, and S (for CZTS) dispersed in non-toxic solvents)
Energy Environ. Sci., 2012, 5, 5340-5345Thin Solid Films, 2003, 431-432, 53-57
Advantages: disadvantages:non-toxic solvents material dispersion
low reaction by-products formulate process
no or low carbon content
Experiments on Inks Type #2ink # Cu (conc.) Zn (conc.) Sn (conc.) Thiourea (conc.) Solvent (volume ratio)
1 Cu(NO3)2 0.8 M Zn(acetate)2 0.5 M SnCl2 0.5 M 4 M H2O:EG=1:1 2 Cu(NO3)2 0.8 M Zn(NO3)2 0.5 M SnCl2 0.5 M 6 M H2O:EG=1:2 3 CuCl 0.8 M Zn(NO3)2 0.5 M SnCl2 0.5 M 6 M H2O:NH4OH:EG=7:4:9 4 CuCl 0.8 M Zn(NO3)2 0.5 M SnCl2 0.5 M 6 M H2O:EtOH =5:1 5 CuCl 0.8 M Zn(NO3)2 0.5 M SnCl2 0.4 M 6 M H2O:EtOH:NH4OH =3:16:1 6 CuCl 0.8 M Zn(NO3)2 0.5 M SnCl2 0.4 M 6 M H2O:EG:NH4OH =3:16:1 7 CuCl 0.8 M Zn(NO3)2 0.5 M SnCl2 0.4 M 6 M H2O:EtOH:NH4OH =3:36:1 8 Cu(NO3)2 0.8 M Zn(NO3)2 0.5 M SnCl2 0.4 M 6 M H2O:EtOH:NH4OH =3:16:1 9 CuCl 0.8 M Zn(NO3)2 0.5 M SnCl2 0.4 M 6 M H2O:IPA:NH4OH =3:16:1 10 Cu(NO3)2 0.8 M Zn(NO3)2 0.5 M SnCl2 0.4 M 6 M H2O:EtOH:NH4OH =3:16:1 11 CuCl 0.8 M Zn(NO3)2 0.5 M SnCl2 0.4 M 6 M H2O:EtOH:HCl=3.8:16:0.2 12 CuCl 0.8 M Zn(NO3)2 0.5 M SnCl2 0.4 M 6 M H2O:EtOH:NH4OH =3.5:16:0.5 13 CuCl 0.8 M Zn(NO3)2 0.5 M SnCl2 0.4 M 6 M H2O:EtOH=1:4 14 CuCl 0.8 M Zn(NO3)2 0.5 M SnCl2 0.4 M 6 M H2O:EtOH:NH4OH=1:1:8 15 CuCl 0.8 M Zn(NO3)2 0.5 M SnCl2 0.4 M 6 M EtOH:NH4OH=4:1
Ethylene glycol (EG) yielded CuS impurity phase, identified by the diffraction peak at 15o in the XRD spectra.
Ink 5 and 8 yielded CZTS crystalline film. However, ink 8 has a short storage time and large aggregation formed after days of storage. Ink 5 is stable and suitable with deposition process, such as spin coating. Again, EG in Ink 6 yielded CuS phase. Inks without XRD were not stable and thus not suitable for making films.Problem: film made by ink 5 is very porous, containing small particles. Tried to solve this issue by collecting particles and re-crystallizing them to form a new film.
Outlook: ink #2 uses thiourea as S source, which brings C content into the film. To avoid this issue, ink type #3 could be a good candidate. Experiment on ink type #3 is undergoing.
Film Fabrication Process Using Formulated Inks