Bulk Heterojunction Active Layer Research Articles

유기물 기반의 새로운 패터닝 기법과 이를 이용한 신재생 에너지 소자

We report on a new patterning technique for organic functional materials applicable to organic photovoltacis (OPVs). The unconventioal patterning technique, plsama-etching selectively perfluoro-alkyl fluorosilanes, is used for producing a bulk-heterojunction active layer with poly(3-hexylthiophene) as the electron donor and [6,6]-phenyl- butyric acid methyl ester as the electron acceptor. The patterning with reduced leakage path and parasitic capacitance suggests a way for fabrication of OPVs with higher energy conversion efficiency.

A Planar Copolymer for High Efficiency Polymer Solar Cells

An alternating copolymer, poly(2-(5-(5,6-bis(octyloxy)-4-(thiophen-2-yl)benzo[c][1,2,5]thiadiazol-7-yl)thiophen-2-yl)-9-octyl-9H-carbazole) (HXS-1), was designed, synthesized, and used as the donor material for high efficiency polymer solar cells. The close packing of the polymer chains in the solid state was confirmed by XRD. A J(sc) of 9.6 mA/cm(2), a V(oc) of 0.81 V, an FF of 0.69, and a PCE of 5.4% were achieved with HXS-1 and [6,6]-phenyl C(71)-butyric acid methyl ester (PC(71)BM) as a bulk heterojunction active layer spin-coated from a solvent mixture of 1,2-dichlorobenzene and 1,8-diodooctane (97.5:2.5) under air mass 1.5 global (AM 1.5 G) irradiation of 100 mW/cm(2).

Three-dimensional nanoscale organization of polymer solar cells

The performance of polymer solar cells (PSCs) strongly depends on the three-dimensional morphological organization of the compounds within the bulk heterojunction active layer. Donor and acceptor materials should form co-continuous networks with nanoscale phase separation to sustain effective dissociation of excitons into free electrons and holes at the donor/acceptor interface and to guarantee fast charge carrier transport from any place in the photoactive layer to the corresponding electrodes. Here, we describe applications of the technique of electron tomography to directly visualize with nanometre resolution and study in detail the 3D organization in the photoactive layers of PSCs, with the aim of identifying the critical morphology parameters contributing to high efficiency of bulk heterojunction systems.

Enhanced photocurrent and efficiency of poly(3-hexylthiophene)/fullerene photovoltaic devices by the incorporation of gold nanoparticles

We have investigated the role of gold nanoparticle incorporated in the bulk-heterojunction active layer of poly(3-hexylthiophene) (P3HT)/fullerene. Since the performance of this organic photovoltaic device is strongly related to the charge carrier transport mobility of bulk heterojunction that arises from the molecular ordering of P3HT semiconductor, we have set the range of nanoparticle concentration to the infinitesimal level, which does not affect the thermally-induced ordering and conductivity of P3HT/fullerene composite film. While the increase of power conversion efficiency is mainly attributed to the enhancement of photocurrent, both the fill factor and the open circuit voltage of photovoltaic device were not sensitive to the concentration of gold nanoparticles, which does not coincide with the previous report on the case of poly(3-octylthiophene)/fullerene/nanoparticle mixture. We suggest that an enhancement of the photoinduced short-circuit current and efficiency can be explained by the increased absorption of nanoparticle–polymer composite film with the condition of the consistent molecular ordering of donor-acceptor bulk-heterojunction. At the weight fraction of 6.25 × 10 −8 for gold nanoparticle/P3HT, about 50% of enhancement ( i.e. from 1.43 to 2.17%) was obtained in the power efficiency.

Improvements of fill factor in solar cells based on blends of polyfluorene copolymers as electron donors

The photovoltaic characteristics of solar cells based on alternating polyfluorene copolymers, poly(2,7-(9,9-dioctyl-fluorene)- alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)) (APFO-3), and poly(2,7-(9,9-didodecyl-fluorene)- alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)) (APFO-4), blended with an electron acceptor fullerene molecule [6,6]-phenyl-C 61-butyric acid methyl ester (PCBM), have been investigated and compared. The two copolymers have the same aromatic backbone structure but differ by the length of their alkyl side chain. The overall photovoltaic performance of the solar cells is comparable irrespective of the copolymer used in the active layer. However, the fill factor (FF) values of the devices are strongly affected by the copolymer type. Higher FF values were realized in solar cells with APFO-4 (with longer alkyl side chain)/PCBM bulk heterojunction active layer. On the other hand, devices with blends of APFO-3/APFO-4/PCBM were found to render fill factor values that are intermediate between the values obtained in solar cells with APFO-3/PCBM and APFO-4/PCBM active film. Upon using APFO-3/APFO-4 blends as electron donors, the cell efficiency can be enhanced by about 16% as compared to cells with either APFO-3 or APFO-4. The transport of holes in each polymer obeys the model of hopping transport in disordered media. However, the degree of energetic barrier against hopping was found to be larger in APFO-3. The tuning of the photovoltaic parameters will be discussed based on studies of hole transport in the pure polymer films, and morphology of blend layers. The effect of bipolar transport in PCBM will also be discussed.