Doojin Vak

Toward Large Scale Roll‐to‐Roll Production of Fully Printed Perovskite Solar Cells

Fully printed perovskite solar cells are demonstrated with slot-die coating, a scalable printing method. A sequential slot-die coating process is developed to produce efficient perovskite solar cells and to be used in a large-scale roll-to-roll printing process. All layers excluding the electrodes are printed and devices demonstrate up to 11.96% power conversion efficiency. It is also demonstrated that the new process can be used in roll-to-roll production.

Fabrication of organic bulk heterojunction solar cells by a spray deposition method for low-cost power generation

The authors report on a spray deposition method as a cost-efficient technique for the fabrication of organic solar cells (OSCs). Active layers of OSCs were fabricated using conventional handheld airbrushes. Although the spray deposited film showed a relatively rougher surface than spin coated ones, pinhole-free and constant thickness films could be obtained. An optimized OSC showed 2.83% of power conversion efficiency and 52% of incident photon to current conversion efficiency even though the device was fabricated in air. The performance of sprayed OSCs was comparable to that of the spin coated devices fabricated in air.

Organic Solar Cells Using a High‐Molecular‐Weight Benzodithiophene–Benzothiadiazole Copolymer with an Efficiency of 9.4%

A high molecular weight donor-acceptor conjugated polymer is synthesized using the Suzuki polycondensation method. Using this polymer, a single-junction bulk-heterojunction solar cell is fabricated giving a power conversion efficiency of 9.4% using a fullerene-modified ZnO interlayer at the cathode contact.

Surface plasmon enhanced photoluminescence of conjugated polymers

To produce surface plasmons, silver nanostructures were fabricated using a thermal evaporation method and the surface plasmon wavelength was tuned via an annealing. These nanostructures were located between the indium tin oxide (ITO) and poly(3,4-ethylenedioxy thiophene)/poly(styrenesulfonate) for the coupling of the surface plasmon resonance with organic fluorophores. To prevent the quenching of emission, spacer was placed between the light emitting polymers and the ITO substrate. As a result, the authors were able to observe an increase in photoluminescence of conjugated polymers using the silver nanostructures.

Factors to be Considered in Bulk Heterojunction Polymer Solar Cells Fabricated by the Spray Process

One of the attractions of solution-processed polymer solar cells (PSCs) is the potential for low-cost production by high-throughput roll-to-roll processes. The spray process can be suggested as an elegant alternative for PSCs fabrication due to its high production speed. We highlight the effects of sprayed droplet sizes on the film topography and drying time of droplets. We relate the latter to the PSCs device performances. The transfer efficiency and deposition rate of the spray process as a function of the droplet size are investigated for the high production speed and lowering the cost. PSC device fabrication with an optimized spray-operating condition yielded a power conversion efficiency of 3.4%. The comparable efficiency of PSCs fabricated by a roll-to-roll compatible process compared to spin-coated one achieved in this paper brings these devices one step closer to the realization of low-cost PSCs production.

A novel azobenzene-based amorphous molecular material with a spiro linked bifluorene

A novel, high Tg azobenzene-based amorphous molecular material, spiro-ADA, was designed and synthesized via a palladium catalyzed amination reaction. The introduction of bulky spiro linked bifluorene with the non-planar structure of triphenylamine of spiro-ADA prevented crystallization of the molecules and led to good amorphous film formation and thermal stability with a high glass transition temperature of 147 °C. Photoinduced behavior such as optically induced birefringence, diffraction efficiency, and surface relief gratings (SRGs) were investigated in relation to their unique molecular structures. Because of the high concentration of azobenzene groups and a low molecular mass, the films showed a very rapid response to linearly polarized light, a high diffraction efficiency of 38.7%, and a large modulation depth of around 320 nm. In addition, the thermal stability of SRGs inscribed on the spiro-ADA film was measured and found to be very stable below Tg despite its low molar mass and the absence of any chain entanglement.

A porphyrin-hexa-peri-hexabenzocoronene-porphyrin triad: synthesis, photophysical properties and performance in a photovoltaic device

Hexa-peri-hexabenzocoronene (HBC) is a discotic polycyclic aromatic hydrocarbon with good charge transport characteristics while the light harvesting property of porphyrins is well-known. In order to take advantage of the properties of both materials, a porphyrin-hexa-peri-hexabenzocoronene-porphyrin triad 6 was synthesised for the first time. In photoluminescence studies, the emission from the higher energy HBC unit was completely quenched by the porphyrin unit indicating efficient energy transfer. This novel hybrid material 6 was tested in bulk heterojunction photovoltaic devices reaching a power conversion efficiency of 1.2%.

Synthesis of novel arylamine containing perfluorocyclobutane and its electrochromic properties

A new electrochromic oligomer based on an arylamine compound containing a perfluorocyclobutane (PFCB) ring has been synthesized via 2 + 2 cyclodimerization. A new N,N,N′,N′-tetraphenyl-biphenyl-4,4′-diamine (TPD) with PFCB (TPD-PFCB) showed high thermal stability with a decomposition temperature (Td) of 435 °C. Cyclic voltammograms of TPD-PFCB films coated onto an indium–tin oxide substrate showed two reversible redox steps during a potential scan between 0.7 and 1.2 V. The spectroelectrochemical series of TPD-PFCB films exhibited color change from colorless to yellow and then to greenish blue during the oxidation reaction of TPD-PFCB. This oligomer exhibited a high electrochromic coloration efficiency (602 cm2/C) and a comparable response speed (coloring and bleaching time at 700 nm were 0.71 and 0.12 s, respectively).

Characterization of a high-thermal-stability spiroanthracenefluorene-based blue-light-emitting polymer optical gain medium

We report the solid-state optical gain characteristics of a spiroanthracenefluorene polymer, namely, poly(9-spiro(10,10-bis(2-ethylhexyl)-10H-anthracene)fluorene) (PEHSAF), specifically designed for thermal stability. An efficient stimulated emission occurs at λ=445nm under amplified spontaneous emission conditions for asymmetric slab waveguide structures. The modal gain and propagation loss coefficients were found to be g⩽38cm−1 and α=0.8cm−1, respectively. The PEHSAF stimulated emission characteristics are shown to be thermally stable in vacuo for temperatures up to 250 °C. Surface-emitting distributed feedback lasers have been fabricated by spin-coating PEHSAF onto one-dimensional grating structures. The lasers operate in the blue spectral region and exhibit low oscillation thresholds (⩾18nJ) and relatively high slope efficiencies (⩽5%). Varying the PEHSAF film thickness allows the tuning of the emission wavelength within a 16 nm window.

Differentially pumped spray deposition as a rapid screening tool for organic and perovskite solar cells

We report a spray deposition technique as a screening tool for solution processed solar cells. A dual-feed spray nozzle is introduced to deposit donor and acceptor materials separately and to form blended films on substrates in situ. Using a differential pump system with a motorised spray nozzle, the effect of film thickness, solution flow rates and the blend ratio of donor and acceptor materials on device performance can be found in a single experiment. Using this method, polymer solar cells based on poly(3-hexylthiophene) (P3HT):(6,6)-phenyl C61 butyric acid methyl ester (PC61BM) are fabricated with numerous combinations of thicknesses and blend ratios. Results obtained from this technique show that the optimum ratio of materials is consistent with previously reported values confirming this technique is a very useful and effective screening method. This high throughput screening method is also used in a single-feed configuration. In the single-feed mode, methylammonium iodide solution is deposited on lead iodide films to create a photoactive layer of perovskite solar cells. Devices featuring a perovskite layer fabricated by this spray process demonstrated a power conversion efficiencies of up to 7.9%.