Methods of making non-covalently bonded carbon-titania nanocomposite thin films and applications of the same
In one aspect of the invention, a dye sensitized solar cell has a counter-electrode including carbon-titania nanocomposite thin films made by forming a carbon-based ink; forming a titania (TiO 2 ) solution; blade-coating a mechanical mixture of the carbon-based ink and the titania solution onto a substrate; and annealing the blade-coated substrate at a first temperature for a first period of time to obtain the carbon-based titania nanocomposite thin films. In certain embodiments, the carbon-based titania nanocomposite thin films may include solvent-exfoliated graphene titania (SEG-TiO 2 ) nanocomposite thin films, or single walled carbon nanotube titania (SWCNT-TiO 2 ) nanocomposite thin films.
1. A solvent-exfoliated graphene titania (SEG-TiO 2 ) nanocomposite thin film made by a method comprising:
forming a concentrated SEG ink containing SEG, ethyl-cellulose (EC) and terpineol;
forming a titania solution containing titanium dioxide (TiO 2 );
blade-coating a mechanical mixture of the concentrated SEG ink and the titania solution containing TiO 2 onto a substrate; and
annealing the blade-coated substrate at a predetermined temperature for a third period of time to obtain the SEG-TiO 2 nanocomposite thin film,
wherein the SEG-TiO 2 nanocomposite thin film comprises a homogenous structure and a porous network of SEG nanoplatelets decorated with TiO 2 particles, wherein the SEG nanoplatelets and the TiO 2 particles are non-covalently bonded to each other in the SEG-TiO 2 nanocomposite thin film, wherein the SEG nanoplatelets are characterized with a first intensity ratio of a peak intensity at a D-band at about 1350 cm −1 to a peak intensity at a G-band at about 1590 cm −1 of a Raman spectrum of the SEG nanoplatelets, which is a measure of a relative concentration of sp 3 hybridized defects compared to sp 2 hybridized graphene domains, wherein the first intensity ratio has an average value of 0.17, wherein the SEG-TiO 2 nanocomposite thin film comprises 0.25-0.55 weight % of the SEG, and wherein a second intensity ratio of a peak intensity at a D-band at about 1350 cm −1 to a peak intensity at a G-band at about 1590 cm −1 of a Raman spectrum of the SEG-TiO 2 nanocomposite thin film is less than 1.
2. The SEG-TiO 2 nanocomposite thin film of claim 1 , wherein the first amount is about 2-3 g, and the second amount is about 40-60 ml.
3. The SEG-TiO 2 nanocomposite thin film of claim 1 , wherein the first period of time is about 2.5-3.5 hours; the second period of time is about 3-6 hours; the third period of time is about 20-45 minutes; the predetermined frequency is about 30-50 kHz; a predetermined rotation speed is about 6000-9000 rpm; and the predetermined temperature is about 350-450° C.
4. The SEG-TiO 2 nanocomposite thin film of claim 1 , wherein the titania solution comprises a titanium dioxide P25 ink.
5. The SEG-TiO 2 nanocomposite thin film of claim 1 , wherein the titania solution comprises a titania nanosheet (TiNS) ink.
6. The SEG-TiO 2 nanocomposite thin film of claim 5 , wherein the forming of the TiNS ink comprises:
mixing a third amount of titanium butoxide with a fourth amount of hydrofluoric acid for about 20-45 minutes to form a mixed solution;
heating the mixed solution at about 175-225° C. for about 20-28 hours under hydrothermal conditions; and
rinsing the heated mixed solution to obtain the TiNS ink.
7. The SEG-TiO 2 nanocomposite thin film of claim 6 , wherein the third amount is about 15-25 ml, and the fourth amount is about 2.5-3.2 ml.
8. The SEG-TiO 2 nanocomposite thin film of claim 1 , wherein the SEG nanoplatelets have lateral dimensions ranging from about 50 nm to 750 nm.
9. The SEG-TiO 2 nanocomposite thin film of claim 1 , wherein the TiO 2 particles have an average diameter of about 21 nm.
10. The SEG-TiO 2 nanocomposite thin film of claim 1 , wherein the step of forming the concentrated SEG ink comprises:
adding a first amount of natural graphite to a second amount of N,N-dimethylforamide (DMF) to form a graphite solution;
sonicating the graphite solution at a predetermined frequency for a first period of time;
centrifuging the sonicated graphite solution for a second period of time at a predetermined rotation speed to obtain a SEG supernatant; and
disposing the SEG supernatant in ethyl-cellulose (EC) and terpineol, and evaporating the DMF in the SEG supernatant to form the concentrated SEG ink.
11. The SEG-TiO 2 nanocomposite thin film of claim 1 , wherein the step of forming the concentrated SEG ink comprises:
adding a first amount of natural graphite to a second amount of an ethyl-cellulose (EC)-ethanol solution to form a graphite solution;
sonicating the graphite solution at a predetermined frequency for a first period of time;
centrifuging the sonicated graphite solution for a second period of time at a predetermined rotation speed to obtain a SEG supernatant; and
disposing the SEG supernatant in terpineol to perform solvent exchange and to form the concentrated SEG ink.