To increase the open circuit voltage (VOC) of polymer solar cells (PSCs) based on polythiophene, two new ester group functionalized polythiophene derivatives, PCTDT and PCTBDT, were designed and synthesized via alternating copolymerization of thiophene‐3‐carboxylate (CT) with the 2,2′‐bithiophene (DT) and benzodithiophene (BDT) units, respectively. The resulting copolymers exhibited broad and strong absorptions in the visible region, which was similar to that of the commonly used poly(3‐hexylthiophene) (P3HT). Through cyclic voltammetry measurements, it was found that both copolymers showed lower HOMO energy levels (−5.27 eV for PCTDT and −5.36 eV for PCTBDT) than that of P3HT (−5.03 eV), indicating that the HOMO energy level could be efficiently reduced by introducing the ester group into the polymer side chain. Photovoltaic properties of the copolymers blended with [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) as electron acceptor were investigated. The obtained two devices possessed both relatively large short circuit current (ISC) and higher VOC than that of P3HT:PCBM blend. For PCTBDT:PCBM blend, a power conversion efficiency (PCE) up to 2.32%, an ISC of 6.94 mA · cm−2, and a VOC of 0.80 V were observed while PCTDT:PCBM system demonstrated a PCE of 1.75% with a VOC of 0.68 V.
Charge transfer behavior of Poly(3‐hexylthiophene) (P3HT) and [6,6]‐phenyl‐C61‐butyric acid methyl eser (PCBM) in solutions and in films were examined by photoluminescence (PL) spectroscopy. PL study in solutions indicated that separation distance between P3HT and PCBM affected charge transfer efficiency more seriously than the interface area issue between P3HT and PCBM. P3HT/PCBM film showed very effective photo‐induced charge transfer before post‐thermal annealing on the bi‐layer P3HT/PCBM film. Charge transfer efficiency was gradually diminished by the annealing‐induced phase separation between P3HT and PCBM as revealed by increasing PL emission intensity of P3HT. 相似文献
Two small molecules named PI‐DPP and NI‐DPP with a DPP core as the central strong acceptor unit and phthalimide/naphthalimide as the terminal weak acceptor were designed and synthesized. The effects of terminal phthalimide/naphthalimide units on the thermal behavior, optical and electrochemical properties, as well as the photovoltaic performance of these two materials were systematically studied. Cyclic voltammetry revealed that the lowest unoccupied molecular orbitals (LUMO) (~ ‐3.6 eV) of both molecules were intermediate to common electron donor (P3HT) and acceptor (PCBM). This indicated that PI‐DPP and NI‐DPP may uniquely serve as electron donor when blended with PCBM, and as electron acceptor when blended with P3HT, where sufficient driving forces between DPPs and PCBM, as well as between P3HT and DPPs should be created for exciton dissociation. Using as electron donor materials, PI‐DPP and NI‐DPP devices exhibited low power conversion efficiencies (PCEs) of 0.90% and 0.76% by blending with PCBM, respectively. And a preliminary evaluation of the potential of the NI‐DPP as electron acceptor material was carried out using P3HT as a donor material, and P3HT: NI‐DPP device showed a PCE of 0.6%, with an open circuit voltage (V OC) of 0.7 V, a short circuit current density (J SC) of 1.91 mA•cm‐2, and a fill factor (FF) of 45%. 相似文献
To maximize the efficiency of heterojunction organic photovoltaics (HJOPVs), it is imperative to increase not only the open-circuit
voltage (VOC) but also the short-circuit current (ISC). Therefore, it is desirable to find an organic acceptor material that possesses a higher lowest unoccupied molecular orbital
(LUMO) level for higher VOC and can absorb photons in the solar spectrum efficiently for larger ISC. In this paper, in comparison with the typical donor poly(3-hexylthiophene) (P3HT) and acceptor [6,6]-phenyl-C61-butyric acid ester ([60]PCBM), the geometries, electronic structures, absorption spectra, and transport properties of a series
of organic compounds containing 9,9′-bifluorenylidene (9,9′BF) were systematically investigated using density functional and the semiclassical Marcus charge transfer theory calculation
to evaluate their potential severing as acceptor. Our results indicate that the absorption spectra of 99′BF derivatives have better overlap with the solar spectrum than those of [60]PCBM, and higher LUMOs result in a significant
enhancement of VOC when they are used in HJOPVs with P3HT as donor materials. On the other hand, these compounds own higher electron carrier
mobilities comparing with [60]PCBM. The study also demonstrates that the H-shaped compounds based on the 99′BF backbone possess good photophysical and charge transport properties, can be promising organic semiconductor for heterojunction
photovoltaics. 相似文献
Effect of the device fabrication conditions on photovoltaic performance of the polymer solar cells based on poly(3‐hexylthiophene) (P3HT) as donor and indene‐C70 bisadduct (IC70BA) as acceptor was studied systematically. The device fabrication conditions we studied include pre‐thermal annealing temperature, active layer thickness, and the P3HT:IC70BA weight ratios. For devices with a 188‐nm‐thick active layer of P3HT:IC70BA (1:1, w:w) blend film and pre‐thermal annealing at 150°C for 10 min, maximum power conversion efficiency (PCE) reached 5.82% with Voc of 0.81 V, Isc of 11.37 mA/cm2, and FF of 64.0% under the illumination of AM1.5G, 100 mW/cm2. 相似文献
Spin‐coating a mixture solution of P3HT and PCBM on a cold substrate largely enhanced the power conversion efficiency (PCE) of the bulk heterojunction (BHJ) solar cells. This concept was based on the abrupt decrease in the solubility of P3HT as solution temperature decreased. The selective precipitation of P3HT on the PEDOT:PSS‐coated cold substrate facilitated a desirable rich composition of P3HT at the interface with the PEDOT:PSS layer. The high crystallinity of P3HT suppressed the movement of PCBM during thermal annealing, preventing aggregation of PCBM. The morphological excellence of the pristine film gave a comparable PCE to that made by the conventional fabrication process. After thermal annealing, the device made via coating on a cold substrate showed above 30% increase in PCE from the BHJ solar cells made by the conventional method.
Vinyl addition homo‐ and copolymerization of norbornene monomer ( M1 ) functionalized with a PCBM moiety using a Pd(II) catalyst in combination with a 1‐octene chain transfer agent efficiently produces polynorbornenes with side‐chain PCBM groups. Characterization by NMR spectroscopy and elemental analysis reveals that the copolymers constitute a well‐defined polymer structure with controlled incorporation of M1 . Although the homopolymer is insoluble in organic solvents, the copolymers containing 62 mol% ( P2 ) and 50 mol% ( P3 ) of the PCBM moiety are soluble in chlorinated solvents such as o‐dichlorobenzene. The bulk‐heterojunction organic photovoltaic devices fabricated based on the P3HT: P3 blends show that P3 can adequately function as an electron acceptor, leading to a cell with a power conversion efficiency of 1.5%, which is outstanding among the polymeric rivals. 相似文献
A series of poly{(3‐hexylthiophene)‐co‐[3‐(6‐hydroxyhexyl)thiophene]}:titania (P3HT‐OH:TiO2) hybrids were synthesized via the in situ polycondensation of titanium (IV) n‐butoxide in the presence of P3HT‐OH. Introducing a hydroxyl moiety onto the side‐chain of poly(3‐hexylthiophene) (P3HT) significantly promotes the polymer‐titania interaction, resulting in the formation of homogeneous hybrid colloids. The UV‐vis spectra of P3HT‐OH:TiO2 films demonstrate that TiO2 markedly affects the stacking structure and the chain conformation of P3HT‐OH. The maximum absorption wavelength of these hybrid materials can be tailor‐made by merely varying the weight percentage of TiO2. Moreover, P3HT‐OH:TiO2 can be further utilized as an efficient compatibilizer in preparing photoactive P3HT:P3HT‐OH:TiO2 films with excellent miscibility. The photovoltaic cell based on such a hybrid exhibited a 2.4‐fold higher value of power‐conversion efficiency compared to the cell based on P3HT:TiO2.
Polymer solar cells were fabricated based on composite films of poly(2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐1,4‐phenylenevinylene) (MEH‐PPV):fullerene derivative (6,6)‐phenyl‐C61‐butyric acid methyl ester (PCBM) with weight blend ratio of 1:3, 1:4 and 1:5, spin‐coated from chloroform (CF), chlorobenzene (CB), and o‐dichlorobenzene (ODCB) solutions, respectively. Photoinduced current and power conversion efficiency (PCE) of the devices show a dependence on the solvents. The solar cells have the highest PCE at 1:5 blend ratio. Transmission electron microscopy (TEM) morphology reveals that there are some voids in MEH‐PPV:PCBM films. The void number decreases with the solvent from CF to CB and ODCB. We found the voids are located at the bottom of the films through electron tomography technique by TEM and film bottom‐side morphology study by atomic force microscopy. The charge carrier transport efficiency and collection efficiency should decrease greatly due to the voids, and the more voids the film has, the more degree the efficiencies decrease. PCE of the solar cell prepared from CF is lower than that of the solar cells prepared from CB and ODCB. The void phenomenon of MEH‐PPV:PCBM based solar cell and method to investigate the void position provide an experimental evidence and research mentality to fabricate polymer solar cell with high performance. 相似文献