Jaejung Ko

Perovskite Solar Cells with 12.8% Efficiency by Using Conjugated Quinolizino Acridine Based Hole Transporting Material

A low band gap quinolizino acridine based molecule was designed and synthesized as new hole transporting material for organic-inorganic hybrid lead halide perovskite solar cells. The functionalized quinolizino acridine compound showed an effective hole mobility in the same range of the state-of-the-art spiro-MeOTAD and an appropriate oxidation potential of 5.23 eV vs the vacuum level. The device based on this new hole transporting material achieved high power conversion efficiency of 12.8% under the illumination of 98.8 mW cm(-2), which was better than the well-known spiro-MeOTAD under the same conditions. Moreover, this molecule could work alone without any additives, thus making it to be a promising candidate for solid-state photovoltaic application.

N-Doped graphene nanoplatelets as superior metal-free counter electrodes for organic dye-sensitized solar cells.

Highly efficient counter electrodes (CEs) for dye-sensitized solar cells (DSSCs) were developed using thin films of scalable and high-quality, nitrogen-doped graphene nanoplatelets (NGnP), which was synthesized by a simple two-step reaction sequence. The resultant NGnP was deposited on fluorine-doped SnO2 (FTO)/glass substrates by using electrospray (e-spray) coating, and their electrocatalytic activities were systematically evaluated for Co(bpy)3(3+/2+) redox couple in DSSCs with an organic sensitizer. The e-sprayed NGnP thin films exhibited outstanding performances as CEs for DSSCs. The optimized NGnP electrode showed better electrochemical stability under prolonged cycling potential, and its Rct at the interface of the CE/electrolyte decreased down to 1.73 Ω cm(2), a value much lower than that of the Pt electrode (3.15 Ω cm(2)). The DSSC with the optimized NGnP-CE had a higher fill factor (FF, 74.2%) and a cell efficiency (9.05%), whereas those of the DSSC using Pt-CE were only 70.6% and 8.43%, respectively. To the best of our knowledge, the extraordinarily better current-voltage characteristics of the DSSC-NGnP outperforming the DSSC-Pt for the Co(bpy)3(3+/2+) redox couple (in paticular, FF and short circuit current, Jsc) is highlighted for the first time.

Efficient and stable panchromatic squaraine dyes for dye-sensitized solar cells

A new series of stable, unsymmetrical squaraine near-IR sensitizers (JK-216 and JK-217), which are assembled using both thiophenyl pyrrolyl and indolium groups, exhibit a panchromatic light harvesting up to 780 nm. The JK-216 based cell exhibited a record efficiency of 6.29% for near-IR DSSCs. In addition, the JK-217 device showed an excellent stability under a light soaking test at 60 °C for 1000 h.

Ordered multimodal porous carbon as highly efficient counter electrodes in dye-sensitized and quantum-dot solar cells.

Ordered multimodal porous carbon (OMPC) was explored as a counter electrode in ruthenium complex dye-sensitized solar cells (DSSCs) and CdSe quantum-dot solar cells (QDSCs). The unique structural characteristics such as large surface area and well-developed three-dimensional (3-D) interconnected ordered macropore framework with open mesopores embedded in the macropore walls make the OMPC electrodes have high catalytic activities and fast mass transfer kinetics toward both triiodide/iodide and polysulfide electrolytes. The efficiency (ca. 8.67%) of the OMPC based DSSC is close to that (ca. 9.34%) of the Pt based one. Most importantly, the QDSC employing OMPC material presents a high efficiency of up to 4.36%, which is significantly higher than those of Pt- and activated carbon based solar cells, ca. 2.29% and 3.30%, respectively.

High Molar Extinction Coefficient Organic Sensitizers for Efficient Dye-Sensitized Solar Cells

We have designed and synthesized highly efficient organic sensitizers with a planar thienothiophene-vinylene-thienothiophene linker. Under standard global AM 1.5 solar conditions, the JK-113-sensitized cell gave a short circuit photocurrent density (J(sc)) of 17.61 mA cm(-2), an open-circuit voltage (V(oc)) of 0.71 V, and a fill factor (FF) of 72%, corresponding to an overall conversion efficiency (eta) of 9.1%. The incident monochromatic photo-to-current conversion efficiency (IPCE) of JK-113 exceeds 80% over the spectral region from 400 to 640 nm, reaching its maximum of 93% at 475 nm. The band tails off toward 770 nm, contributing to the broad spectral light harvesting. Solar-cell devices based on the sensitizer JK-113 in conjunction with a volatile electrolyte and a solvent-free ionic liquid electrolyte gave high conversion efficiencies of 9.1% and 7.9%, respectively. The JK-113-based solar cell fabricated using a solvent-free ionic liquid electrolyte showed excellent stability under light soaking at 60 degrees C for 1000 h.

Stepwise Cosensitization of Nanocrystalline TiO2 Films Utilizing Al2O3 Layers in Dye‐Sensitized Solar Cells

Keywords: aluminum oxide ; electron transfer ; hole transfer ; sensitizers ; titanium dioxide ; Efficient Co-Sensitization ; Organic Sensitizers ; Recombination Dynamics ; Charge Recombination ; Highly Efficient ; Blocking Layers ; Electrodes ; Dendrimers ; Cyanine Reference EPFL-ARTICLE-160552doi:10.1002/anie.200802852View record in Web of Science Record created on 2010-11-30, modified on 2016-08-09

Spherical polypyrrole nanoparticles as a highly efficient counter electrode for dye-sensitized solar cells

Discrete spherical polypyrrole (PPy) nanoparticles with a uniform diameter of ∼85 nm and electrical conductivity of ∼10 S cm−1 were fabricated by chemical oxidative polymerization within micelles composed of myristyl trimethyl ammonium bromide (MTAB) and decyl alcohol as the nanoreactors. A methanol-based colloidal dispersion containing 5 wt% PPy was dropcast directly onto fluorine-doped tin oxide (FTO) glass to use as counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). The surface resistivity of the PPy layer on the FTO glass decreased from 624 to 387 Ω sq−1 after post-doping with concentrated HCl vapor for 1 min. The DSSCs made of PPy/FTO and HCl-doped PPy/FTO CEs exhibited power conversion efficiencies of ∼5.28 and ∼6.83%, respectively under standard AM 1.5 sunlight illumination. The post-doped and highly oxidized PPy allowed the electrons to move into the PPy layer readily and facilitated the electrocatalytic reaction of the I3−/I− redox couple, giving enhanced cell performance. Moreover, the cell efficiency was enhanced to ∼7.73% with further fine tuning of the electrolyte composition, which is comparable to the value (∼8.2%) using conventional Pt CEs.

A polymer gel electrolyte to achieve ≥6% power conversion efficiency with a novel organic dye incorporating a low-band-gap chromophore

A quasi-solid-state dye-sensitized solar cell with novel organic sensitizers incorporating a benzothiadiazole chromophore showed excellent long-term stability, which exhibited 10% decrease during the 1000 h light soaking; the optimized cell gave a short circuit photocurrent density of 12.03 mA cm−2, an open circuit voltage of 0.720 V and a fill factor of 0.76, corresponding to an overall conversion efficiency of 6.61% under standard global AM 1.5 solar conditions.

Hierarchical nanostructured spherical carbon with hollow core/mesoporous shell as a highly efficient counter electrode in CdSe quantum-dot-sensitized solar cells

Hierarchical nanostructured spherical carbon with hollow core/mesoporous shell (HCMS) was explored as a counter electrode in CdSe quantum-dot-sensitized solar cells. Compared with conventional Pt electrodes and commercially available activated carbon, the HCMS carbon counter electrode exhibits a much larger fill factor due to the considerably decreased charge transfer resistance at the interface of the counter electrode/polysulfide electrolyte. Furthermore, a solar cell with the HCMS carbon counter electrode presents a high power conversion efficiency of up to 3.90% as well as an incident photon-to-current conversion efficiency peak of 80%.

Direct nitrogen fixation at the edges of graphene nanoplatelets as efficient electrocatalysts for energy conversion

Nitrogen fixation is essential for the synthesis of many important chemicals (e.g., fertilizers, explosives) and basic building blocks for all forms of life (e.g., nucleotides for DNA and RNA, amino acids for proteins). However, direct nitrogen fixation is challenging as nitrogen (N2) does not easily react with other chemicals. By dry ball-milling graphite with N2, we have discovered a simple, but versatile, scalable and eco-friendly, approach to direct fixation of N2 at the edges of graphene nanoplatelets (GnPs). The mechanochemical cracking of graphitic C−C bonds generated active carbon species that react directly with N2 to form five- and six-membered aromatic rings at the broken edges, leading to solution-processable edge-nitrogenated graphene nanoplatelets (NGnPs) with superb catalytic performance in both dye-sensitized solar cells and fuel cells to replace conventional Pt-based catalysts for energy conversion.