Il Jeon

Direct and Dry Deposited Single-Walled Carbon Nanotube Films Doped with MoOx as Electron-Blocking Transparent Electrodes for Flexible Organic Solar Cells

UNLABELLED Organic solar cells have been regarded as a promising electrical energy source. Transparent and conductive carbon nanotube film offers an alternative to commonly used ITO in photovoltaics with superior flexibility. This communication reports carbon nanotube-based indium-free organic solar cells and their flexible application. Direct and dry deposited carbon nanotube film doped with MoO(x) functions as an electron-blocking transparent electrode, and its performance is enhanced further by overcoating with PEDOT PSS. The single-walled carbon nanotube organic solar cell in this work shows a power conversion efficiency of 6.04%. This value is 83% of the leading ITO-based device performance (7.48%). Flexible application shows 3.91% efficiency and is capable of withstanding a severe cyclic flex test.

Mixture of [60] and [70]PCBM giving morphological stability in organic solar cells

Mix-PCBM, comprising [6,6]-phenyl-C61-butyric acid methyl ester (PC60BM) and [6,6]-phenyl-C71-butyric acid methyl ester (PC70BM), is a promising acceptor material for use in organic solar cells with higher device stability and cost performance. The inverted photovoltaic device using poly(3-hexylthiophene) (P3HT) and mix-PCBM exhibited a power conversion efficiency (PCE) of 3.34% (open-circuit voltage = 0.63 V, short-circuit current density = 8.55 mA/cm2, and fill factor = 0.60), slightly higher than that using P3HT and PC60BM (PCE = 3.27%). More importantly, the mix-PCBM device was more stable to heating at 150 °C than the PC60BM device, due to little morphological change, which was characterized by atomic force microscope and light absorption measurements.

Metal-electrode-free Window-like Organic Solar Cells with p-Doped Carbon Nanotube Thin-film Electrodes.

Organic solar cells are flexible and inexpensive, and expected to have a wide range of applications. Many transparent organic solar cells have been reported and their success hinges on full transparency and high power conversion efficiency. Recently, carbon nanotubes and graphene, which meet these criteria, have been used in transparent conductive electrodes. However, their use in top electrodes has been limited by mechanical difficulties in fabrication and doping. Here, expensive metal top electrodes were replaced with high-performance, easy-to-transfer, aerosol-synthesized carbon nanotubes to produce transparent organic solar cells. The carbon nanotubes were p-doped by two new methods: HNO3 doping via ‘sandwich transfer’, and MoOx thermal doping via ‘bridge transfer’. Although both of the doping methods improved the performance of the carbon nanotubes and the photovoltaic performance of devices, sandwich transfer, which gave a 4.1% power conversion efficiency, was slightly more effective than bridge transfer, which produced a power conversion efficiency of 3.4%. Applying a thinner carbon nanotube film with 90% transparency decreased the efficiency to 3.7%, which was still high. Overall, the transparent solar cells had an efficiency of around 50% that of non-transparent metal-based solar cells (7.8%).

Air-processed inverted organic solar cells utilizing a 2-aminoethanol-stabilized ZnO nanoparticle electron transport layer that requires no thermal annealing

Correction for ‘Air-processed inverted organic solar cells utilizing a 2-aminoethanol-stabilized ZnO nanoparticle electron transport layer that requires no thermal annealing’ by Il Jeon et al., J. Mater. Chem. A, 2014, 2, 18754–18760.

Carbon-sandwiched perovskite solar cell

Promising perovskite solar cell technology with soaring power conversion efficiencies has the common problems of low stability and high cost. This work provides a solution to these problems by employing a carbon sandwich structure, in which the fullerene bottom layer solves the stability issue and the carbon nanotube top electrode layer offers the merits of having high stability and being low-cost. Devices fabricated using different hole-transporting materials infiltrated into carbon nanotube networks were examined for their performance and stability under constant illumination in air. Polymeric hole-transporting layers show much higher stability when combined with carbon nanotubes due to their compact nature and stronger interaction with the carbon network. As a result, the encapsulated device showed high stability both in air and under light illumination, maintaining up to 80% of the initial efficiency after 2200 hours under actual operation conditions. Cost analysis also shows that using the polymeric hole-transporting materials in carbon nanotube films brings the fabrication cost down to less than 5.5% that of conventional devices. Our study proposes a promising cell structure toward highly stable and low-cost perovskite photovoltaic technologies for the future.

Enhancement of Low-field Magnetoresistance in Self-Assembled Epitaxial La0.67Ca0.33MnO3:NiO and La0.67Ca0.33MnO3:Co3O4 Composite Films via Polymer-Assisted Deposition.

Polymer-assisted deposition method has been used to fabricate self-assembled epitaxial La0.67Ca0.33MnO3:NiO and La0.67Ca0.33MnO3:Co3O4 films on LaAlO3 substrates. Compared to pulsed-laser deposition method, polymer-assisted deposition provides a simpler and lower-cost approach to self-assembled composite films with enhanced low-field magnetoresistance effect. After the addition of NiO or Co3O4, triangular NiO and tetrahedral Co3O4 nanoparticles remain on the surface of La0.67Ca0.33MnO3 films. This results in a dramatic increase in resistivity of the films from 0.0061 Ω•cm to 0.59 Ω•cm and 1.07 Ω•cm, and a decrease in metal-insulator transition temperature from 270 K to 180 K and 172 K by the addition of 10%-NiO and 10%-Co3O4, respectively. Accordingly, the maximum absolute magnetoresistance value is improved from −44.6% to −59.1% and −52.7% by the addition of 10%-NiO and 10%-Co3O4, respectively. The enhanced low-field magnetoresistance property is ascribed to the introduced insulating phase at the grain boundaries. The magnetism is found to be more suppressed for the La0.67Ca0.33MnO3:Co3O4 composite films than the La0.67Ca0.33MnO3:NiO films, which can be attributed to the antiferromagnetic properties of the Co3O4 phase. The solution-processed composite films show enhanced low-field magnetoresistance effect which are crucial in practical applications. We expect our polymer-assisted deposited films paving the pathway in the field of hole-doped perovskites with their intrinsic colossal magnetoresistance.

Room temperature-processed inverted organic solar cells using high working-pressure-sputtered ZnO films

This study reports improved performance of inverted organic solar cells by using high working-pressure sputtered ZnO. Sputtering produces highly crystalline ZnO without the need for thermal annealing. However, photovoltaic devices fabricated by using sputtered ZnO have shown lower power conversion efficiencies than those made by using sol–gel ZnO. On the other hand, sol–gel ZnO limits the flexible application of inverted organic solar cells because of high-temperature annealing. Therefore, a new method of sputtering under high working pressure is developed. The power conversion efficiency of inverted organic solar cells fabricated using this high working-pressure-sputtered ZnO (η = 8.6%, VOC = 0.77 V, JSC = 15.6 mA cm−2, and FF = 0.72) is superior to that of conventional sol–gel ZnO-based devices (η = 7.8%, VOC = 0.73 V, JSC = 16.0 mA cm−2, and FF = 0.63). Furthermore, utilizing the low temperature process of sputtering, flexible application is successfully achieved using polyethylene terephthalate indium tin oxide films.

Single-Walled Carbon Nanotubes in Solar Cells

Photovoltaics, more generally known as solar cells, are made from semiconducting materials that convert light into electricity. Solar cells have received much attention in recent years due to their promise as clean and efficient light-harvesting devices. Single-walled carbon nanotubes (SWNTs) could play a crucial role in these devices and have been the subject of much research, which continues to this day. SWNTs are known to outperform multi-walled carbon nanotubes (MWNTs) at low densities, because of the difference in their optical transmittance for the same current density, which is the most important parameter in comparing SWNTs and MWNTs. SWNT films show semiconducting features, which make SWNTs function as active or charge-transporting materials. This chapter, consisting of two sections, focuses on the use of SWNTs in solar cells. In the first section, we discuss SWNTs as a light harvester and charge transporter in the photoactive layer, which are reviewed chronologically to show the history of the research progress. In the second section, we discuss SWNTs as a transparent conductive layer outside of the photoactive layer, which is relatively more actively researched. This section introduces SWNT applications in silicon solar cells, organic solar cells, and perovskite solar cells each, from their prototypes to recent results. As we go along, the science and prospects of the application of solar cells will be discussed.

Engineering high-performance and air-stable PBTZT-stat-BDTT-8:PC61BM/PC71BM organic solar cells

High-performance air-stable PBTZT-stat-BDTT-8 organic solar cells were fabricated using mixed C60/C70 fullerene acceptors. Normal-architecture devices using PBTZT-stat-BDTT-8 with PC71BM produced a power conversion efficiency (PCE) of 9.38%. An inverted-architecture, which possesses higher stability, was fabricated using a more economical PC61BM and PC71BM mixture with solution-processed PEDOT:PSS on top and produced a PCE of 8.15%. Exploiting the viscous nature of PBTZT-stat-BDTT-8, the slow evaporation effect was utilised to achieve an even higher efficiency of 8.73%. A stability test was conducted under operating conditions and our devices showed remarkably higher stability compared with PTB7-based devices.

Fullerene-Cation-Mediated Noble-Metal-Free Direct Introduction of Functionalized Aryl Groups onto [60]Fullerene

Aryl[60]fullerenyl cations (ArC60+), which were generated by heating aryl[60]fullerenyl dimers (ArC60-C60Ar) to generate aryl[60]fullerenyl radicals (ArC60•) followed by oxidation using Cu(II) salts (Cu(BF4)2(aq)), were reacted with various functionalized aryl boronic acids to produce functionalized 1,4-diaryl[60]fullerenes. This protocol tolerated various functional groups, such as OH, NH2, COCH3, and Cl substituents, with yields reaching 93%. C60Ar1Ar2 (Ar2 = p-NH2C6H4) was used as a dopant in a photoactive CH3NH3PbI3 layer of a perovskite solar cell.