Complexation Chemistry in N,N-Dimethylformamide-Based Molecular Inks for Chalcogenide Semiconductors and Photovoltaic Devices
[1];
[2];
[1]
- Department of Chemical Engineering, Clean Energy Institute, Molecular Engineering &, Sciences Institute, University of Washington, Seattle, Washington 98195-1750, United States
- Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999, Richland, Washington 99352, United States
Molecular inks based on dimethyl sulfoxide, thiourea, and metal salts may be used to form high optoelectronic quality semiconductors and have led to high power conversion efficiencies for solution-processed photovoltaic devices for Cu2ZnSn(S,Se)4(CZTS), Cu2Zn(Ge,Sn)(S,Se)4(CZGTS), CuIn(S,Se)2(CIS) and Cu(In,Ga)(S,Se)2 (CIGS). However, several metal species of interest including Ag(I), In(III), Ge(II), and Ge(IV) have either low solubility (requiring dilute inks) or lead to precipitation or gelation. Here, we demonstrate that the combination of N,N-Dimethylformamide (DMF) and thiourea (TU) has the remarkable ability to form intermediate-stability acid-base complexes with a wide number of metal chloride Lewis acids (CuCl, AgCl, ZnCl2, InCl3, GaCl3, SnCl4, GeCl4, and SeCl4) to form high-concentration stable molecular inks. Using calorimetry, Raman spectroscopy, and solubility experiments, we reveal the important role of chloride transfer and thiourea to stabilize metal cations in DMF. Methylation of thiourea is used to vary the strength of the Lewis basicity and demonstrate that the strength of the thiourea:metal chloride complex formed after DMF evaporation is critical to prevent volatilization of metal containing species. Further, we formulated a sulfur-free molecular ink which was used to deposit photoluminescent, crystalline CuInSe2 without selenization . Finally, we demonstrate the ability of the DMF-TU molecular ink chemistry to lead to high photovoltaic power conversion efficiencies and high open-circuit voltages for solution-processed CIS and CZGTS with PCE’s of 13.4% and 11.0% and Voc/Voc,SQ of 67% and 63%, respectively.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1496810
- Report Number(s):
- PNNL-SA-136834
- Journal Information:
- Journal of the American Chemical Society, Vol. 141, Issue 1; ISSN 0002-7863
- Publisher:
- American Chemical Society (ACS)
- Country of Publication:
- United States
- Language:
- English
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