Wenfei Shen

Novel donor–acceptor polymers containing o-fluoro-p-alkoxyphenyl-substituted benzo[1,2-b:4,5-b′]dithiophene units for polymer solar cells with power conversion efficiency exceeding 9%

In this work, a new electron-rich building block, o-fluoro-p-alkoxyphenyl-substituted benzo[1,2-b:4,5-b′]dithiophene (BDT) unit, has been used to construct donor (D)–acceptor (A) conjugated copolymers with electron-deficient units 5,6-difluoro-4,7-di(4-(2-ethylhexyl)-2-thienyl)-2,1,3-benzothiadiazole (C8DTBTff) and 5,6-difluoro-4,7-di(4-hexyl-2-thienyl)-2,1,3-benzothiadiazole (C6DTBTff), named P-o-FBDTP-C8DTBTff (P2) and P-o-FBDTP-C6DTBTff (P3), respectively. The experimental results indicate that the incorporation of fluorine into the ortho-position of the alkoxyphenyl substituted BDT unit can enable its resultant polymer to efficiently tune the energy levels and improve the mobility of the derived bulk heterojunction layer, which results in a much higher power conversion efficiency (PCE) of P2 (8.10%). Moreover, replacing the 2-ethylhexyl chains on the DTBTff unit with hexyl chains can improve the planarity of the conjugated backbone of the polymer, which makes the P3/PC71BM blends exhibit higher carrier mobility than P2/PC71BM. Finally, a PCE of 9.02% for the device of P3 is obtained without any additive treatment, which is the highest value achieved for the widely reported D–A polymers with fluorine substituted BDT as the electron-donor unit in single junction polymer solar cells.

Facile preparation of TiOX film as an interface material for efficient inverted polymer solar cells

Titanium oxide (TiOX) is an effective electron transport layer in polymer solar cells (PSCs). Here, we report an efficient inverted polymer solar cell based on P3HT and fullerenes using a high density, single-step solution processed amorphous TiOX (α-TiOX) film as an electron transport layer. The α-TiOX film was prepared by spin coating tetrabutyl titanate (TBT) isopropanol solution onto ITO coated glass in a glovebox filled with N2 and then annealing at different temperatures in air. The films with high light transmittance are very smooth. The PSCs with the α-TiOX electron transport layer showed enhanced photovoltaic performance in comparison with the device using PEDOT:PSS as the anode buffer layer. The optimized power conversion efficiency (PCE) of the PSCs based on P3HT/PC61BM and P3HT/PC71BM with the α-TiOX electron transport layer reached 4.25% and 4.65%, respectively, under AM1.5G illumination (100 mW cm−2). In addition, the PSCs with the α-TiOX electron transport layer exhibited good stability. The results indicate that facile preparation of α-TiOX films using cheap TBT is promising for high-efficiency PSCs and large-scale fabrication of flexible electronics.

Efficient polymer solar cells based on a new benzo[1,2-b:4,5-b ']dithiophene derivative with fluorinated alkoxyphenyl side chain

A novel fluorine-containing benzo[1,2-b:4,5-b′]dithiophene (BDT) derivative (BDTPF) was designed to construct a donor–acceptor (D–A)-structured polymer (PBDTPF-DTBT) with the electron-withdrawing unit 4,7-di(4-(2-ethylhexyl)-2-thienyl)-2,1,3-benzothiadiazole (DTBT). The resulting polymer exhibits a broad absorption spectrum, relatively low lying HOMO energy level (−5.39 eV) and a good film-forming ability. The field-effect mobility of PBDTPF-DTBT is 0.034 cm2 V−1 s−1. Bulk heterojunction organic solar cells (OSCs) based on PBDTPF-DTBT and PC71BM were prepared and showed a good photovoltaic performance with power conversion efficiency (PCE) of 7.02%. This work demonstrates that a BDT unit with fluorinated alkoxyphenyl side chains is a promising candidate as an electron-rich building block for high performance solution-processed OSCs.

The effect of pore structure of activated carbon on the adsorption of Congo red and vitamin B12

Abstract The mesopore content of a commercial activated carbon was increased by catalytic activation over various metal oxides. The adsorption of VB12 and Congo red was measured to investigate the effect of pore structure upon the adsorption property. It was found that both the pore size distribution and the pore volume play key roles in determining the adsorption properties. The wider the pore size was, the shorter of time reaching equilibrium was. Higher pore volume gave higher adsorption capacity.

2D expanded conjugated polymers with non-fullerene acceptors for efficient polymer solar cells

Non-fullerene polymer solar cells (PSCs) have attracted great attention due to their good optical absorption and convenient structure modification. Some small molecular acceptors such as ITIC have exhibited excellent photovoltaic performance. Based on these acceptors, it is very important to screen donor materials to further improve the performance. The benzotriazole-based polymer is an important type of donor material, especially for non-fullerene PSCs. We have designed and synthesized a type of benzotriazole-based conjugated polymer with a 2D expanded side chain. These polymers exhibit good crystallinity in films. Non-fullerene PSC devices based on polymer:ITIC show a PCE of 8.03% with a high JSC of over 17 mA cm−2, which might be attributed to its good crystallinity. This result indicates the advancement of the 2D extended structure in the design of a high performance polymer.

Strong Enhancement of Photoelectric Conversion Efficiency of Co-hybridized Polymer Solar Cell by Silver Nanoplates and Core–Shell Nanoparticles

A new way was meticulously designed to utilize the localized surface plasmon resonance (LSPR) effect and the light scattering effect of silver nanoplate (Ag-nPl) and core-shell Ag@SiO2 nanoparticles (Ag@SiO2-NPs) to enhance the photovoltaic performances of polymer solar cells (PSCs). To prevent direct contact between silver nanoparticles (Ag-NPs) and photoactive materials which will cause electrons quenching, bare Ag-nPl were spin-coated on indium tin oxide and silica capsulated Ag-NPs were incorporated to a PBDTTT-C-T:PC71BM active layer. As a result, the devices incorporated with Ag-nPl and Ag@SiO2-NPs showed great enhancements. With the dual effects of Ag-nPl and Ag@SiO2-NPs in devices, all wavelength sensitization in the visible range was realized; therefore, the power conversion efficiency (PCE) of PSCs showed a great enhancement of 14.0% to 8.46%, with an increased short-circuit current density of 17.23 mA·cm-2. The improved photovoltaic performances of the devices were ascribed to the LSPR effect and the light scattering effect of metallic nanoparticles. Apart from optical effects, the charge collection efficiency of PSCs was improved after the incorporation of Ag-nPl.

Incorporating a vertical BDT unit in conjugated polymers for drastically improving the open-circuit voltage of polymer solar cells

In order to search for new wide band gap materials, vertical benzodithiophene (BDT) is designed as an electron donating unit to construct D–A type conjugated polymers. Two polymers PVB1 and PVB2 were synthesized by the Stille coupling reaction with benzothiadiazole (BT) and thieno[3,4-c]pyrrole-4,6-dione (TPD) as the accepting moieties, respectively. These polymers show wide optical band gaps of over 2.0 eV and low HOMO energy levels of below −5.5 eV. Polymer solar cell (PSC) devices were fabricated using the above polymers as donors and fullerene derivatives as acceptors. PSCs based on PVB1 and PC71BM showed a power conversion efficiency (PCE) of 2.84% with a Voc of 1.00 V, a Jsc of 6.80 mA cm−2 and a FF of 0.42. And PSCs based on PVB2 and PC71BM showed a PCE of 2.05% with a Voc of 1.09 V, a Jsc of 5.33 mA cm−2 and a FF of 0.35. Both polymers showed a high Voc of over 1.0 V, which should be attributed to the deep-lying HOMO levels of the polymers. They would be potential candidates as wide band gap components to construct tandem solar cells.

Preparation of mesoporous carbon by steam activation of commercial activated carbon in the presence of yttrium oxide

Abstract Mesoporous carbon was prepared by steam activation of commercial activated carbon in the presence of yttrium oxide. The loading of yttrium nitrate (precursor of yttrium oxide) was 0.2, 0.6, 1.0 and 2.0 wt%. The weight lost and gases formed during heating were detected by using thermogravimetric analysis and mass spectroscopy. The surface area and the total volume of the mesoporous carbon were determined by the nitrogen adsorption. The pore size distribution was calculated by the BJH method. With the increase of activation temperature, the reaction became faster and the pore formed was wider and the pore size distribution became scatter. The pore diameter and volume increase with the increasing of the loading of yttrium oxide.