Preparation And Photovoltaic Properties Of Poly(3-hexylthiophene) And Carbon Microspheres Composite Films

As a result of the increasing consumption and environmental pollution of fossil fuel, new substitute energy sources are explored. Among them, solar energy, with a bright exploitative prospect, is a renewable, clear, and new energy source. Organic photovoltaic devices offering a promising technology to harvest solar energy are candidates for low-cost source of low carbon electricity. Recently, polymer solar cells based on electron-donating conjugated polymers and electron-accepting carbon materials have attracted public attention. Although the carbon film materials, including carbon nanotubes, fullerenes and graphenes, have recently achieved breakthrough in the performance of solar cells, the power conversion efficiency (PCE) is low and the cost is high. Carbon microspheres (CMSs) as fullerene-like material, have simple preparation process, low preparation cost, good electroconductivity and stable chemical properties, are expected to have excellent photovoltaic characteristics. However insolubility of CMSs in water and organic solvents restricts their wide application. So, polymer solar cells with functionally modified CMSs as the electron acceptor, and P3HT as the electron donor were prepared, in order to further reduce the cost and improve efficiency.On the basis of the theoretical research regarding surface properties of double layer CMSs, relationship between energy structure of CMSs and photoelectric property was primarily investigated by theoretical calculation. Then, CMSs were oxidized by a mixture of concentrated sulfuric acid and nitric acid (ratio of3:1by volume) in order to synthesize oxidized-CMSs (O-CMSs). O-CMSs was further modified with1,6-hexanediamine and dodecylamine to prepare two kinds of aminated CMSs (Al-CMSs and A2-CMSs, respectively) through investigating the influences of N, N’-dicyclohexyl carbodiimide (DCC) dosage, reaction time and reaction temperature on the product, to improve their compatability in solvent and matchability in energy level with electron-donor poly (3-hexylthiophene). P3HT:O-CMSs, P3HT:Al-CMSs and P3HT:A2-CMSs composite films were prepared by blending and spin-coating method with O-CMSs, Al-CMSs or A2-CMSs and P3HT mixture chloroform solution, in which the influences of blend ratio, speed of spin-coating, concentrations of spin-coating and annealing were discussed. The optical performances of three kinds of composite films were investigated. The relevant organic photovoltaic cells were prepared to test photoelectric property of P3HT:O-CMSs, P3HT:Al-CMSs and P3HT:A2-CMSs active layers. Finally, a kind of excellent acceptor of O-CMSs, Al-CMSs or A2-CMSs matching P3HT was gained. The main conclusions are as follows:1. With double layer CMSs (C6O@C24o), density functional theory (DFT) was used to calculated structure, band gap change and frontier molecular orbital of C6o@C24o grafted different number of carboxyl groups. Results show that grafting organic groups improved the surface properties of the system, and the bonding properties determined the energy level of the system, the band gap and corresponding optical properties.2. Al-CMSs and A2-CMSs had regular morphology when the DCC dosage, amination time and temperature were0.3g/0.3g O-CMSs,36h,110℃and0.4g/0.2g O-CMSs,24h,70℃. The oxidation, HAD and DDA amination of CMSs improved the dispersion of CMSs and energy level structure. There kinds of modified CMSs, energy level-matching with P3HT, were effective acceptor. The sequence of LUMO energy level was A2-CMSs>Al-CMSs>O-CMSs, which favored an increased Voc. 3. P3HT:CMSs (P3HT:O-CMSs, P3HT:Al-CMSs and P3HT:A2-CMSs) composite films coated from30mg/mL CMSs and30mg/mL P3HT, with volume ratio of1:1, under2500rpm, had excellent dispersibility, few surface defects, good absorptivity and high fluorescence quenching, resulting in more overlap with the solar spectrum and effective exciton separation; Annealing treatment on three kinds of heterojunction composite films P3HT:A2-CMSs, P3HT:Al-CMSs and P3HT:O-CMSs improved ordering of P3HT and the crystallization of the composite films, which eventually improved the photovoltaic performances of polymer solar cells. After annealing, the sequence of performance of cells was P3HT:A2-CMSs> P3HT:Al-CMSs> P3HT:O-CMSs. Finally, A2-CMSs matching P3HT as a kind of excellent acceptor was gained.