Here comes the sun: A conversion efficiency as high as 5.4 % has been achieved on dye‐sensitized ZnO solar cells with photoelectrode films consisting of polydisperse aggregates, compared to 2.4 % for ...the films with only nanosized crystallites. The aggregation of nanocrystallites with a broad size distribution is effective in enhancing the light‐harvesting efficiency by inducing light scattering within the photoelectrode films.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
This paper presents a comprehensive review of the literature on one-dimensional (1D) nanostructures (nanowires, nanoribbons, nanotubes, nanobelts, and nanofibers) of π-conjugated small molecules, ...oligomers, and polymers. The diverse methods used in assembling the molecular building blocks into 1D functional nanostructures and nanodevices are discussed, including hard and soft template-assisted synthesis, electrospinning, nanolithography, self-assembly in solution and at interfaces, physical vapor transport, and other strategies. Optical, charge transport, electronic, and photoconductive properties of nanowires and nanotubes of selected classes of π-conjugated molecular systems are discussed next, highlighting unique features of the 1D nanostructures compared to 2D thin films. Overview of applications of these 1D organic nanostructures ranging from nanoscale light-emitting diodes, field-emission devices, organic photovoltaics, sensors/biosensors, spin-electronics, and nanophotonics to nanoelectronics is then given. The final section provides our brief concluding comments on the status of the field and on areas of outstanding challenges and opportunities for future work. We believe that the emerging confluence of nanoscience and organic semiconductors will greatly enrich both fields while leading to enhanced performance in organic electronics and affordable nanotechnologies.
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Light scattering is a method that has been employed in dye-sensitized solar cells for optical absorption enhancement. In conventional dye-sensitized solar cells, large TiO
2
particles with sizes ...comparable to the wavelength of visible light are used as scatterers by either being mixed into the nanocrystalline film to generate light scattering or forming a scattering layer on the top of the nanocrystalline film to reflect the incident light, with the aim to extend the traveling distance of incident light within the photoelectrode film. Recently, hierarchical nanostructures, for example nanocrystallite aggregates (among others), have been applied to dye-sensitized solar cells. When used to form a photoelectrode film, these hierarchical nanostructures have demonstrated a dual function: providing large specific surface area; and generating light scattering. Some other merits, such as the capability to enhance electron transport, have been also observed on the hierarchically structured photoelectrode films. Hierarchical nanostructures possessing an architecture that may provide sufficient internal surface area for dye adsorption and meanwhile may generate highly effective light scattering, make them able to create photoelectrode films with optical absorption significantly more efficient than the dispersed nanoparticles used in conventional dye-sensitized solar cells. This allows reduction of the thickness of the photoelectrode film and thus lowering of the charge recombination in dye-sensitized solar cells, making it possible to increase further the efficiency of existing dye-sensitized solar cells.
This paper reviews the applications of light scattering in DSCs over the past two decades and some recent progress in this topic.
Organic electrochemical transistors (OECTs) hold promise for developing a variety of high‐performance (bio‐)electronic devices/circuits. While OECTs based on p‐type semiconductors have achieved ...tremendous progress in recent years, n‐type OECTs still suffer from low performance, hampering the development of power‐efficient electronics. Here, it is demonstrated that fine‐tuning the molecular weight of the rigid, ladder‐type n‐type polymer poly(benzimidazobenzophenanthroline) (BBL) by only one order of magnitude (from 4.9 to 51 kDa) enables the development of n‐type OECTs with record‐high geometry‐normalized transconductance (gm,norm ≈ 11 S cm−1) and electron mobility × volumetric capacitance (µC* ≈ 26 F cm−1 V−1 s−1), fast temporal response (0.38 ms), and low threshold voltage (0.15 V). This enhancement in OECT performance is ascribed to a more efficient intermolecular charge transport in high‐molecular‐weight BBL than in the low‐molecular‐weight counterpart. OECT‐based complementary inverters are also demonstrated with record‐high voltage gains of up to 100 V V−1 and ultralow power consumption down to 0.32 nW, depending on the supply voltage. These devices are among the best sub‐1 V complementary inverters reported to date. These findings demonstrate the importance of molecular weight in optimizing the OECT performance of rigid organic mixed ionic–electronic conductors and open for a new generation of power‐efficient organic (bio‐)electronic devices.
n‐Type organic electrochemical transistors (OECTs) underperform compared to p‐type OECTs. By tuning the molecular weight of the rigid ladder‐type poly(benzimidazobenzophenanthroline), n‐type OECTs with record‐high figures of merit are reported. OECT‐based complementary inverters are also demonstrated with high voltage gains of up to 100 V V−1 and ultralow power consumption down to 0.32 nW, depending on the supply voltage.
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Poly(3-butylthiophene) (P3BT) nanowires, prepared by solution-phase self-assembly, have been used to construct highly efficient P3BT/fullerene nanocomposite solar cells. The fullerene/P3BT ...nanocomposite films showed an electrically bicontinuous nanoscale morphology with average field-effect hole mobilities as high as 8.0 × 10−3 cm2/Vs due to the interconnected P3BT nanowire network revealed by TEM and AFM imaging. The power conversion efficiency of fullerene/P3BT nanowire devices was 3.0% (at 100 mW/cm2, AM1.5) in air and found to be identical with our similarly tested fullerene/poly(3-hexylthiophene) photovoltaic cells. This discovery expands the scope of promising materials and architectures for efficient bulk heterojunction solar cells.
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A high molecular weight alternating naphthalene diimide–bithiophene copolymer (poly{N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl-alt-5,5′-(2,2′-bithiophene)} ...(PNDIOD-T2)) has been prepared by direct (hetero)arylation polymerization (DHAP). Its structure and properties were investigated in comparison with the Stille-prepared commercial analog, N2200. It was found that the new DHAP-derived PNDIOD-T2 and known N2200 have similar optical absorption spectra and HOMO/LUMO energy levels but slightly different 1H NMR spectra. Inverted all-polymer solar cells using PNDIOD-T2 as the acceptor and PCE12 or PCE10 as the donor polymer showed slightly superior performances compared to similar N2200 devices. All-polymer solar cells with 7.3% efficiency could be achieved with PNDIOD-T2 blends without the use of a processing additive. These results demonstrate that low-cost and eco-friendly DHAP-based n-type semiconducting polymers are promising for developing high performance all-polymer solar cells.
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High‐performance ambipolar transistors and inverters are demonstrated using a new donor–acceptor copolymer semiconductor. The ambipolar transistors show electron and hole mobilities of up to 0.04 and ...0.003 cm2 V−1 s−1, respectively. Voltage transfer curves of the inverters made on common gold electrodes showed sharp switching with gain of 30.
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The performance of bulk heterojunction solar cells made from blends of a non‐fullerene acceptor, N,N′‐bis(2‐ethylhexyl)‐2,6‐bis(5″‐hexyl‐2,2′;5′,2″terthiophen‐5yl)‐1,4,5,8‐naphthalene diimide ...(NDI‐3TH), and poly(3‐hexylthiophene) (P3HT) donor is enhanced 10‐fold by using a processing additive in conjunction with an electron‐blocking and a hole‐blocking buffer layers. The power conversion efficiency of P3HT:NDI‐3TH solar cells improves from 0.14% to 1.5% by using a processing additive (1,8‐diiodooctane) at an optimum concentration of 0.2 vol%, which is far below the 2‐3 vol% optimum concentrations found in polymer/fullerene systems. TEM and AFM imaging show that the size and connectivity of the NDI‐3TH domains in the phase‐separated P3HT:NDI‐3TH blends vary strongly with the concentration of the processing additive. These results demonstrate, for the first time, that processing additives can be effective in the optimization of the morphology and performance of bulk heterojunction polymer solar cells based on non‐fullerene acceptors.
The power conversion efficiency of bulk heterojunction polymer solar cells based on a non‐fullerene acceptor is enhanced 10‐fold from 0.14 to 1.5% by using a processing additive in conjunction with an electron‐blocking and a hole‐blocking buffer layers. The morphology and device performance vary significantly with the concentration of the processing additive, reaching an optimum at 0.2 vol%, which is far lower than 2‐3 vol% found in polymer/fullerene systems.
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A series of nine alternating donor–acceptor copolymer semiconductors based on naphthalene diimide (NDI) acceptor and seven different thiophene moieties with varied electron-donating strength and ...conformations has been synthesized, characterized, and used in n-channel and ambipolar organic field-effect transistors (OFETs). The NDI copolymers had moderate to high molecular weights, and most of them exhibited moderate crystallinity in thin films and fibers. The LUMO energy levels of the NDI copolymers, at −3.9 to −3.8 eV, were constant as the donor moiety was varied. However, the HOMO energy levels could be tuned over a wide range from −5.3 eV in P8 to −5.9 eV in P1 and P3. As semiconductors in n-channel OFETs with gold source/drain electrodes, the NDI copolymers exhibited good electron transport with maximum electron mobility of 0.07 cm2/(V s) in P5. Although head-to-head (HH) linkage induced backbone torsion, polymer P4 showed substantial electron mobility of 0.012 cm2/(V s) in bottom-gate/top-contact device geometry. Some of the copolymers with high-lying HOMO levels (P7 and P8) exhibited ambipolar charge transport in OFETs with high electron mobilities (0.006–0.02 cm2/(V s)) and significant hole mobilities (>10–3 cm2/(V s)). Varying the device geometry from top-contact to bottom-contact leads to the appearance or enhancement of hole transport in P4, P6, P7, and P8. Copolymers with smaller alkyl side chains on the imide group of NDI have enhanced carrier mobilities than those with bulkier alkyl side chains. These results show underlying structure–property relationships in NDI-based copolymer semiconductors while demonstrating their promise in n-channel and ambipolar transistors.
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Conducting polymers, such as the p-doped poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), have enabled the development of an array of opto- and bio-electronics devices. However, ...to make these technologies truly pervasive, stable and easily processable, n-doped conducting polymers are also needed. Despite major efforts, no n-type equivalents to the benchmark PEDOT:PSS exist to date. Here, we report on the development of poly(benzimidazobenzophenanthroline):poly(ethyleneimine) (BBL:PEI) as an ethanol-based n-type conductive ink. BBL:PEI thin films yield an n-type electrical conductivity reaching 8 S cm
, along with excellent thermal, ambient, and solvent stability. This printable n-type mixed ion-electron conductor has several technological implications for realizing high-performance organic electronic devices, as demonstrated for organic thermoelectric generators with record high power output and n-type organic electrochemical transistors with a unique depletion mode of operation. BBL:PEI inks hold promise for the development of next-generation bioelectronics and wearable devices, in particular targeting novel functionality, efficiency, and power performance.
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