Sanghyun Paek

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.

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.

Supersensitization of CdS Quantum Dots with a Near-Infrared Organic Dye: Toward the Design of Panchromatic Hybrid-Sensitized Solar Cells

The photoresponse of quantum dot solar cells (QDSCs) has been successfully extended to the near-IR (NIR) region by sensitizing nanostructured TiO(2)-CdS films with a squaraine dye (JK-216). CdS nanoparticles anchored on mesoscopic TiO(2) films obtained by successive ionic layer adsorption and reaction (SILAR) exhibit limited absorption below 500 nm with a net power conversion efficiency of ~1% when employed as a photoanode in QDSC. By depositing a thin barrier layer of Al(2)O(3), the TiO(2)-CdS films were further modified with a NIR absorbing squaraine dye. Quantum dot sensitized solar cells supersensitized with a squariand dye (JK-216) showed good stability during illumination with standard global AM 1.5 solar conditions, delivering a maximum overall power conversion efficiency (η) of 3.14%. Transient absorption and pulse radiolysis measurements provide further insight into the excited state interactions of squaraine dye with SiO(2), TiO(2), and TiO(2)/CdS/Al(2)O(3) films and interfacial electron transfer processes. The synergy of combining semiconductor quantum dots and NIR absorbing dye provides new opportunities to harvest photons from different regions of the solar spectrum.

Silolothiophene-linked triphenylamines as stable hole transporting materials for high efficiency perovskite solar cells

In this work, we synthesized novel hole transporting materials (HTMs) and studied their impact on the stability of perovskite-based solar cells (PSCs). The steady-state maximum power output of devices in working condition was monitored to assess the stability and predict the lifetime of PSCs prepared using different HTMs. We showed that the HTM has a significant impact on the device lifetime and found that novel silolothiophene linked methoxy triphenylamines (Si-OMeTPAs) enable more stable PSCs. We reported Si-OMeTPA based devices with a half-life of 6 K h, compared to 1 K h collected for the state-of-the-art PSCs using spirofluorene linked methoxy triphenylamines (spiro-OMeTADs) as HTMs. We demonstrated that such a clear improvement is correlated to the superior thermal stability of silolothiophene compared to the spirofluorene linked triphenylamine HTMs.

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.

Highly efficient perovskite solar cells with a compositionally engineered perovskite/hole transporting material interface

Perovskite solar cells (PSCs) have experienced an outstanding advance in power conversion efficiency (PCE) by optimizing the perovskite layer morphology, composition, interfaces, and charge collection efficiency. To enhance PCE, here we developed a new method i.e., engineering a compositional gradient thinly at the rear interface between the perovskite and the hole transporting materials. We demonstrate that charge collection is improved and charge recombination is reduced by formation of an engineered passivating layer, which leads to a striking enhancement in open-circuit voltage (VOC). The passivation effect induced by constructing an additional FAPbBr3−xIx layer on top of the primary (FAPbI3)0.85(MAPbBr3)0.15 film was proven to function as an electron blocking layer within the perovskite film, resulting in a final PCE of 21.3%. Our results shed light on the importance of the interfacial engineering on the rear surface of perovskite layers and describe an innovative approach that will further boost the PSC efficiency.

New type of organic sensitizers with a planar amine unit for efficient dye-sensitized solar cells.

A new type of organic sensitizers incorporating a planar amine unit have been synthesized and demonstrated to be a highly efficient sensitizers, showing evidence of lateral interactions on the TiO(2) surface. Under standard global air mass 1.5 solar conditions, the JK-98 sensitized cell gave a short circuit photocurrent density (J(sc)) of 16.78 mA cm(-2), an open-circuit voltage (V(oc)) of 0.745 V, and a fill factor (ff) of 0.70, corresponding to an overall conversion efficiency (η) of 8.71%.

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.

Synthesis of annulated thiophene perylene bisimide analogues: their applications to bulk heterojunction organic solar cells

Annulated thiophene perylene bisimides and their triphenyl-amine based oligomers have been synthesized. One of the oligomers FPTTPA has been demonstrated to be an efficient electron donor in bulk heterojunction (BHJ) organic solar cells, giving a power conversion efficiency of 1.42%.

Molecular engineering of push-pull chromophore for efficient bulk-heterojunction morphology in solution processed small molecule organic photovoltaics

The synthesis and characterization of new push-pull chromophores, bisDMFA-diTh-CA, bisDMFA-diTh-MMN, and bisDMFA-diTh-MIMN from 5′-(4-(bis(9,9-dimethyl-9H-fluoren-2-yl)aniline (bisDMFA) electron donating, dithiophene bridging, and various electron withdrawing moieties, cyanoacrylic acid (CA), methylene malononitrile (MMN), and methylene indenylidene malononitrile (MIMN), were demonstrated for efficient solution processed BHJ solar cells. The photophysical properties, the hole mobilities from the space charge limitation of current (SCLC) J-V characteristics, and surface morphologies of these materials/PCBM bulk-heterojunction films were also investigated. The best power conversion efficiency of 3.66% (±0.12) with Jsc = 11.82 mA/cm2, FF = 0.35, and Voc = 0.90 V was observed in the BHJ film fabricated with the bisDMFA-diTh-MMN/C71-PCBM composite with 3% 1-chloronaphthalene (CN), which is an efficiency ∼82% and ∼49% higher than before and after post-annealing without treatment of CN, respectively.