Hyeju Choi

Efficient Perovskite Solar Cells with 13.63 % Efficiency Based on Planar Triphenylamine Hole Conductors

A new type of hole transporting material (HTMs) with an incorporated planar amine or triphenylamine as a core unit have been prepared. The two amine derivatives were demonstrated to be efficient hole transporting materials in fabricating solid-state organic-inorganic hybrid solar cells. Perovskite-based solar cells with a planar amine derivative gave a short circuit photocurrent density (Jsc) of 20.98 m Acm(-2), an open circuit voltage (Voc) of 0.972 V, and a fill factor of 0.67, corresponding to an overall conversion efficiency of 13.63 %. The photovoltaic performance is comparable to that of the standard spiro-OMeTAD. Moreover, the device showed good stability under light soaking for 500 h. These HTMs hold promise to replace the expensive spiro-OMeTAD because of their high efficiency, excellent stability, synthesis from simple and inexpensive materials.

Efficient star-shaped hole transporting materials with diphenylethenyl side arms for an efficient perovskite solar cell

Two symmetrical star-shaped hole transporting materials (HTMs), i.e.FA-MeOPh and TPA-MeOPh with a fused triphenylamine or triphenylamine core and diphenylethenyl side arms were synthesized. FA-MeOPh showed a strong molar absorption coefficient and a red-shifted absorption compared with TPA-MeOPh because of its planar configuration. The power conversion efficiency (PCE) of the perovskite solar cells based on FA-MeOPh and TPA-MeOPh is about 11.86% and 10.79%, in which the efficiency of former is comparable to that (12.75%) of spiro-OMeTAD based cell. The high photocurrent (18.39 mA cm−2) of FA-MeOPh based solar cell relative to TPA-MeOPh based one may be attributable to the enhanced absorption in the near-IR region for mp-TiO2/CH3NH3PbI3/HTM based cell. The high mobility and low series resistance of mp-TiO2/CH3NH3PbI3/FA-MeOPh based cell led to the high fill factor (0.698) of FA-MeOPh based solar cell relative to TPA-MeOPh based one (0.627). In addition, the FA-MeOPh based cell showed a relative stability under light soaking for 250 h. The high efficiency, relative stability, synthetically simple and inexpensive materials as the HTMs hold promise to replace the expensive spiro-OMeTAD.

Effect of dopant and clay on nanocomposites of polyaniline (PAN) intercalated into Na+-montmorillonite (Na+-MMT)

The nanocomposites of polyaniline (PAN) and Na + -montmorillonite (Na + - MMT) were synthesized by emulsion polymerization using dodecylbenzenesulfonic acid (DBSA) or camphorsulfonic acid (CSA) as dopant and emulsifier. In the X-ray diffraction patterns of the systems, we observed that the layer of conducting PAN-DBSA or PAN-CSA between the clay layers was in nanoscale layers (< 10 A). The temperature dependence of dc conductivity [σ dc (T)] for the nanocomposites followed a quasi-one dimensional (ID) variable range hopping (VRH) model. The σ dc (T) varied with the dopant used and the molar ratio. From temperature dependent EPR experiments, we obtained the magnetic susceptibility and the line width of the system. The Na + -MMT clay layer plays important role for interchain interaction of the system. The effects of dopant and the layer of Na + -MMT on charge transport and structure are discussed.

Efficient Hole Transporting Materials with Two or Four N,N-Di(4-methoxyphenyl)aminophenyl Arms on an Ethene Unit for Perovskite Solar Cells

Novel steric bulky hole transporting materials (HTMs) with two or four N,N-di(4-methoxyphenyl)aminophenyl units have been synthesized. When the EtheneTTPA was used as a hole transporting material in perovskite solar cell, the power conversion efficiency afforded 12.77 % under AM 1.5 G illumination, which is comparable to the widely used spiro-OMeTAD based solar cell (13.28 %).

Molecular Engineering of Organic Sensitizers with Planar Bridging Units for Efficient Dye‐Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) have received a great deal of attention as low-cost alternatives to conventional p– n junction solar cells. In these cells, the sensitizer is the key component. Although several Ru polypyridyl complexes exhibited high efficiencies above 10 % and long-term stability, they are quite expensive and hard to purify. Recently, the performance of solar cells based on organic sensitizers has been remarkably improved, resulting in impressive efficiencies in the range of 8–10 %. However, one of the drawbacks of organic sensitizers is the sharp and narrow absorption bands of their UV spectra in the blue region, impairing their light-absorption capabilities. Therefore, molecular engineering of organic sensitizers is required in order to broaden and redshift their absorption spectra. A successful approach was achieved through structural modification of the bridged unit. The introduction of a planar p-conjugated unit in the bridged framework is presumed to be the reason for the increase in the spectral response in the red region of the solar spectrum. Although organic-dye-based cells using an I /I3 electrolyte have afforded high power conversion efficiencies, recent studies on replacing the conventional I /I3 electrolyte with a Co/Co electrolyte have received renewed attention. Recently, Yella et al. reported an efficiency of 12.3 % by using a Co/Co electrolyte in conjunction with a porphyrin sensitizer. While high conversion efficiency of 9–10 % has been reached with organic sensitizers and porphyrin dyes using a liquid electrolyte, such as I /I3 or Co/Co redox couple, the stability issue still remains a major challenge due to leakage and evaporation. Accordingly, extensive studies have been conducted to substitute liquid electrolytes with quasi-solid-state or solid-state electrolytes. Herein, we report meticulously designed organic sensitizers incorporating a planar indenoACHTUNGTRENNUNG[1,2-b]thiophene or indenoACHTUNGTRENNUNG[1,2-b]thienoACHTUNGTRENNUNG[2,3-d]thiophene bridging unit to understand the structure–property relationship (Scheme 1). We also investigate the photovoltaic performance of dyes using I /I3 , Co/Co, polymer gel, and solid-state electrolytes.

The impact of an indeno[1,2-b]thiophene spacer on dye-sensitized solar cell performances of cyclic thiourea functionalized organic sensitizers

Two new organic sensitizers (JK-313 and JK-314) possessing bulky cyclic thiourea functionalized triphenylamine as an electron donor were designed and synthesized. Especially, JK-314 showed a strong molar absorption coefficient and a red-shifted absorption compared with JK-313 due to its planar indeno[1,2-b]thiophene spacer. An indeno[1,2-b]thiophene spacer as well as bulky groups on the cyclic thiourea plays a key role in preventing both the intermolecular aggregation and undesired charge recombination in DSSCs, which resulted in an improvement in both short-circuit photocurrent density (Jsc) and open-circuit voltage (Voc). Under standard AM 1.5G solar conditions, JK-314 based DSSCs in the presence of polymer gel electrolytes showed an overall power conversion efficiency (PCE) of 8.44%. It is one of the highest values in organic dye based DSSCs ever reported.

Molecular engineering of organic sensitizers for highly efficient gel-state dye-sensitized solar cells

Three novel organic sensitizers incorporating a planar 4,4-dimethyl-4H-indeno[1,2-b]thiophene or 4,4-dimethyl-4H-indeno[1,2-b]thienothiophene in the bridged group have been designed and synthesized for use in gel-state dye-sensitized solar cells. The photovoltaic performance is quite sensitive to the bridged unit. The optimized cell in JK-276 using a gel electrolyte gave a short circuit photocurrent density of 16.61 mA cm−2, an open circuit voltage of 0.69 V and a fill factor of 0.72, affording an overall conversion efficiency of 8.31% under standard global AM 1.5 solar cell conditions. The efficiency is close to the value of the liquid-state cell (8.40%). The gel-electrolyte cell of JK-276 showed an excellent long-term stability, which remained almost unchanged during the 300 h light soaking test at 70 °C.

Aqueous electrolyte based dye-sensitized solar cells using organic sensitizers

Two novel organic sensitizers containing a 2-(2-methoxyethoxy)ethyl unit are designed and synthesized. Under standard global AM 1.5 solar conditions, the JK-262 sensitized cell in conjunction with an aqueous electrolyte gave a short-circuit photocurrent density (Jsc) of 3.78 mA cm−2, an open-circuit voltage (Voc) of 0.68 V, and a fill factor of 0.82, affording an overall conversion efficiency (η) of 2.10%. The η of JK-262 is higher than that of JK-259 due to the larger Jsc. The improved Jsc value is attributable to the broad and red-shifted absorption band as well as the dense packing of JK-262 on the TiO2 film.

A new unsymmetrical near-IR small molecule with squaraine chromophore for solution processed bulk heterojunction solar cells

A new unsymmetrical low bandgap push–pull squaraine chromophore bis-DMFA-Th-SQ-Th-DCA denoted as JK216D was synthesized and its optical and electrochemical properties (both theoretical and experimental) were investigated. This small molecule having a strong electron withdrawing moiety exhibits a broader absorption band in thin film. The JK216D exhibited suitable highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital energy levels, compatible with that of PC71BM, for efficient photoinduced electron transfer. The bulk heterojunction solar cell fabricated with JK216D:PC71BM (optimized weight ratio of 1:2 and processed with CB) exhibited a PCE of 3.60% (Jsc = 9.97 mA cm−2, Voc = 0.86 V and FF = 0.42). The PCE has been further improved up to 5.25% (Jsc = 11.86 mA cm−2, Voc = 0.82 V and FF = 0.54), when the optimized JK216D:PC71BM (1:2) active layer was processed with the addition of 3 v% 1,8-diiodoctane (DIO) into the CB solution.

Efficient Hole‐Transporting Materials with Triazole Core for High‐Efficiency Perovskite Solar Cells

Efficient hole-transporting materials (HTMs), TAZ-[MeOTPA]2 and TAZ-[MeOTPATh]2 incorporating two electron-rich diphenylamino side arms, through direct linkage or thiophen bridges, respectively, on the C3- and C5-positions of a 4-phenyl-1,2,4-triazole core were synthesized. These synthetic HTMs with donor-acceptor type molecular structures exhibited effective intramolecular charge transfer for improving the hole-transporting properties. The structural modification of HTMs by thiophene bridging might increase intermolecular π-π stacking in the solid state and afford a better spectral response because of their increased π-conjugation length. Perovskite-based cells using TAZ-[MeOTPA]2 and TAZ-[MeOTPATh]2 as HTMs afforded high power conversion efficiencies of 10.9 % and 14.4 %, respectively, showing a photovoltaic performance comparable to that obtained using spiro-OMeTAD. These synthetically simple and inexpensive HTMs hold promise for replacing the more expensive spiro-OMeTAD in high-efficiency perovskite solar cells.