High-performance single-wall carbon nanotube transparent conductive films

doi:10.1016/j.jmst.2019.07.011

Abstract

Abstract:

A single-wall carbon nanotube (SWCNT) has superior optical, electrical, and mechanical properties due to its unique structure and is therefore expected to be able to form flexible high-performance transparent conductive films (TCFs). However, the optoelectronic performance of these films needs to be improved to meet the requirements of many devices. The electrical resistivity of SWCNT TCFs is mainly determined by the intrinsic resistivity of individual SWCNTs and their junction resistance in networks. We analyze these key factors and focus on the optimization of SWCNTs and their networks, which include the diameter, length, crystallinity and electrical type of the SWCNTs, and the bundle size and interconnects in networks, as well as chemical doping and microgrid design. We conclude that isolated/small-bundle, heavily doped metallic or semiconducting SWCNTs with a large diameter, long length and high crystallinity are necessary to fabricate high-performance SWCNT TCFs. A simple, controllable way to construct macroscopic SWCNT networks with Y-type connections, welded junctions or microgrid design is important in achieving a low resistivity. Finally, some insights into the key challenges in the manufacture and use of SWCNT TCFs and their prospects are presented, hoping to shed light on promoting the practical application of SWCNT TCFs in future flexible and stretchable optoelectronics.

Key words: Single-wall carbon nanotube, Transparent conductive film, Junction resistance, Bundle, Doping

Song Jiang, Peng-Xiang Hou, Chang Liu, Hui-Ming Cheng. High-performance single-wall carbon nanotube transparent conductive films[J]. J. Mater. Sci. Technol., 2019, 35(11): 2447-2462.

Figures/Tables 17

Table 1 Performance requirements for the practical applications of TCFs [2].

Application	Minimum T (%)	Maximum R_s (Ω/sq.)
Touch screens	85	500
LCDs	85	100
OLEDs	90	50
PVs	90	10

Table 2 Representative SWCNT TCFs fabricated by wet and dry processes.

Year	Preparation method	R_s (pristine) (Ω/sq.)	Dopant	R_s (doped) (Ω/sq.)	T (%)	FoM (pristine)	FoM (doped)	Ref.
2004	Wet process		HNO₃	30	70		32.2	[6]
2005	Wet process	1000			90	3.5		[24]
2006	Wet process	300	NO₂	100	90	11.6	34.8	[25]
2007	Wet process	175	HNO₃	70	80	9.1	22.8	[26]
2007	Dry process	50			70	19.3		[27]
2008	Wet process	1560	SOCl₂	180	59	0.4	3.5	[28]
2008	Wet process	231			75	5.3		[29]
2009	Wet process	110			80	14.5		[30]
2009	Wet process		HNO₃+ H₂SO₄ or HCl	270	93.5		20.4	[31]
2010	Wet process	187			80	8.5		[33]
2010	Dry process	820	HNO₃	110	90	4.2	31.7	[32]
2011	Wet process		CSA	60	90.9		64.3	[7]
2011	Wet process	600	AuCl₃	36	85	3.7	61.9	[35]
2011	Wet process		HNO₃+ H₂SO₄	133	90		26.2	[36]
2011	Wet process	198	AuCl₃	85	90	17.6	41.0	[34]
2012	Wet process	198.4			81.8	9.0		[38]
2012	Wet process		H₂SO₄	100	90		34.8	[37]
2013	Wet process		HNO₃+ SOCl₂	86	80		18.6	[39]
2013	Wet process		HNO₃	68	89		46.2	[40]
2014	Dry process		HNO₃	160	90		21.8	[42]
2014	Dry process			95	80		16.8	[41]
2014	Dry process (patterning)	300	HNO₃	53	80	5.3	30.1	[41]
2014	Dry process	291	AuCl₃	73	90	12.0	47.7	[54]
2015	Dry process		HNO₃	63	90		55.3	[8]
2015	Wet process	183.6	HNO₃	34	81	9.2	49.9	[44]
2015	Wet process		CuI	55	85		40.5	[45]
2015	Dry process	310			90	11.2		[43]
2016	Dry process	950	HNO₃	89	90	3.7	39.2	[46]
2016	Dry process (patterning)		HNO₃	29	87		90.1	[46]
2016	Dry process		CuCl	98	90		35.6	[47]
2017	Dry process		CuCl₂/ Cu(OH)₂	69.4	90		50.2	[48]
2017	Dry process	250	HNO₃	51	80	6.4	31.3	[49]
2018	Wet process	310			90	11.2		[51]
2018	Dry process	41	HNO₃	25	90	85.0	139.4	[9]
2018	Dry process		AuCl₃	86	90		40.5	[52]
2018	Dry process	195	HNO₃	51	90	17.9	68.3	[50]
2018	Dry process	600	HAuCl₄	40	90	5.8	87.1	[53]

Fig. 1. Representative SWCNT TCF performance since 2004 together with those of ITO TCFs on rigid and flexible substrates, as well as the performance requirements for practical applications in touch screens, LCDs, OLEDs, and PVs.

Fig. 2. Schematic showing the fabrication of SWCNT TCFs by (a) a wet process and (b) a dry process.

Fig. 3. Calculated reflection, transmittance, and absorption of a SWCNT TCF in the broad spectral range from 400 nm to 2 cm [63].

Fig. 4. Conductive atomic force microscopy results on pristine sparse SWCNT networks. (a) Current map of a bundle ～2.3-nm diameter, which overlaps an individual tube of ～1.65-nm diameter. The electrode is positioned on the top of the image (not shown). (b) Local resistance analysis through a bundle and an individual tube depicted as pathways 1 and 2 in the schematic (c). (d) Current map of interconnected tubes of different diameters showing the formation of junctions with different resistances. (e) Local resistance analyzed along an individual tube connected to a sparse configuration of nanotubes highlighted as pathways 1 and 2 in the schematic (f). The electrode is positioned on the left side of the image (not shown) [67].

Fig. 5. Mechanical properties of SWCNT TCFs. (a) Change of R for a SWCNT TCF on a polystyrene substrate fabricated by a wet process under different bending radii (strains). Inset is an optical image of the SWCNT TCF [84]. (b) Change of R for a SWCNT TCF on a poly(dimethylsiloxane) substrate fabricated by a dry process when it was subjected to repeated stretch and release cycles. (c) SEM images of SWCNT TCF under different strains in (b) [83]. (d) Structure of inverted perovskite solar cells based on SWCNT or graphene anodes on plastic substrates. (e) The power conversion efficiency (PCE) change of cells based on SWCNT, graphene, and ITO anodes under different numbers of bending cycles in (d) [49].

Fig. 6. Optical and electrical characterization of CVD, HiPCO, Laser, Arc, and CoMoCat SWCNT samples. (a) Raman spectra (the tube diameters calculated from corresponding radial breathing mode (RBM) peaks are 1.43 nm, 1.35 nm, 1.25 nm, 0.96 nm, and 0.79 nm, respectively) and (b-d) optoelectronic performance [78,85]. The abbreviations refer to SWCNTs synthesized by CVD, HiPCO, laser ablation, arc discharge, and CoMoCat methods, respectively.

Fig. 7. AFM images of CMC-dispersed SWCNTs on a silicon wafer made by (a) 10-minute sonication and (b) 60-minute sonication. (c) Length distribution measured by AFM. (d) Optoelectronic performance of CMC-dispersed SWCNTs [60]. (e) SEM and (f) AFM images of long SWCNTs [89].

Fig. 8. SWCNT film fabrication and characterization of TO and TO-TR samples. (a) Schematic of SWCNT film fabrication. TEM images of (b) TO and (c) TO-TR samples. Contact angle tests with water droplets for (d) TO and (e) TO-TR samples. (f) Optoelectronic performance of different samples [33].

Fig. 9. Conduction of SWCNT networks containing a mixture of m- and s- SWCNTs with different s-SWCNT contents. (a) Conduction mechanism in SWCNT networks versus s-SWCNT content as evaluated from absorption spectra [97]. (b) Simulated conductance of SWCNT networks versus s-SWCNT content. (c) Simulated images of conduction maps as a function of s-SWCNT content [96].

Fig. 10. Preparation and optoelectronic performance of SWCNT TCFs enriched with m-SWCNTs. (a) Picture of the monodispersed SWCNT solution and (b) corresponding absorption spectra. (c) Performance of metallic and unsorted SWCNTs [29]. (d) Etching mechanism used for enriching TCFs with m-SWCNTs. (e) Contents of m-SWCNTs synthesized using different etchant carrier gases. (f) Performance of different samples [42].

Fig. 11. Structures and optoelectronic performance of SWCNT samples. (a) AFM image of isolated SWCNTs [8]. (b) TEM image of carbon-welded isolated SWCNTs. (c) Performance of carbon-welded isolated SWCNT TCFs, other SWCNT TCFs and a reported ITO TCF [9]. SEM images for (d) Arc-I and (e) Arc-II SWCNTs. The Arc-I sample was produced using a longer sonication time and higher centrifugation speed than the Arc-II sample. (f) Performance of Arc-I and Arc-II samples [85].

Fig. 12. Junction resistance statistics of (a) X-type and (b) Y-type contacts [74]. (c) SEM image of Y-type SWNT networks. (d) TEM image of stretched SWCNTs [27]. (e) SEM image of Y-type SWCNT networks [22].

Fig. 13. Structural and electrical characterization of carbon weld. (a) Low- and (b) high-resolution TEM images of isolated SWCNTs with carbon welds. Isolated SWCNT-based FETs (c) without and (d) with carbon weld. (e, f) Ids versus Vds of devices (c) and (d), respectively. Gate voltage Vgs = -10 V [9].

Fig. 14. Effects of chemical doping on SWCNTs. (a) Water bucket model for changing the work function (Fermi level) of SWCNTs by n-doping or p-doping [114]. (b) Work function and Rs changes with increasing AuCl3 concentration. (c) Absorption spectra of SWCNTs doped by different concentrations of AuCl3. (d) Schematic of the energy band change at m- and s-SWCNTs. The leftmost diagram is the energy band before m- and s-SWCNTs contact, and its right is the energy band after m- and s-SWCNTs contact. The others are the energy band changes with increased AuCl3 doping [113].

Fig. 15. Fabrication and characterization of patterned SWCNT TCFs. (a) Schematic of the SWCNT TCF fabrication process with a microgrid. (b) Photograph of a SWCNT TCF with a microgrid. (c) Micrograph of the TCF with a microgrid with a period of 37.5 μm. (d) Optoelectronic performance of SWCNT TCFs with the microgrid for various A values of the grid [41]. (e) Magnified optical image (left) of a patterned SWCNT TCF with a 50-μm spacing and its SEM images (middle and right) [46].

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