Jin Hyuck Heo

Multicolored Organic/Inorganic Hybrid Perovskite Light‐Emitting Diodes

Bright organic/inorganic hybrid perov-skite light-emitting diodes (PrLEDs) are realized by using CH3 NH3 PbBr3 as an emitting layer and self-organized buffer hole-injection layer (Buf-HIL). The PrLEDs show high luminance, current efficiency, and EQE of 417 cd m(-2) , 0.577 cd A(-1) , and 0.125%, respectively. Buf-HIL can facilitate hole injection into CH3 NH3 PbBr3 as well as block exciton quenching.

Highly efficient low temperature solution processable planar type CH3NH3PbI3 perovskite flexible solar cells

The current density–voltage (J–V) hysteresis and power conversion efficiency (η) of planar type CH3NH3PbI3 perovskite solar cells with TiO2 and ZnO electron conductors, which are formed by high temperature spray pyrolysis deposition at 450 °C and by room temperature spin-coating and subsequent heat-treatment at 150 °C, respectively, were compared. The ZnO based perovskite solar cells exhibited better efficiency deviation (15.96 ± 1.07%) and less J–V hysteresis than the TiO2 based cells (15.20 ± 1.23%) because the ZnO based cell has 1.2 fold longer charge carrier life time (τn) than the ZnO based cell and the ZnO electron conductor has better electron conductivity (0.0031 mS cm−1) than the TiO2 electron conductor (0.00006 mS cm−1), thereby balancing the electron flux and the hole flux more. Due to the low temperature solution processability of the ZnO electron conductor, we could demonstrate a highly efficient PEN (poly-ethylenenaphthalate)/ITO/ZnO/CH3NH3PbI3 perovskite/PTAA/Au flexible planar solar cell with 1.1 V open-circuit voltage (Voc), 18.7 short-circuit current density (mA cm−2) Jsc, 75% fill factor (FF), and 15.4% η for the forward scan direction and 1.1 V Voc, 18.7 mA cm−2Jsc, 76% FF and 15.6% η for the reverse scan direction under illumination of 1 Sun.

CH3 NH3 PbBr3 -CH3 NH3 PbI3 Perovskite-Perovskite Tandem Solar Cells with Exceeding 2.2 V Open Circuit Voltage.

Perovskite-perovskite tandem solar cells with open-circuit voltages of over 2.2 V are reported. These cost-effective, solution-processible perovskite hybrid tandem solar cells with high open-circuit voltages are fabricated by the simple lamination of a front planar MAPbBr3 perovskite cell and a back MAPbI3 planar perovskite solar cell.

Stable semi-transparent CH3NH3PbI3 planar sandwich solar cells

Semi-transparent CH3NH3PbI3 (MAPbI3) planar sandwich solar cells could be fabricated by simply laminating an FTO (F doped tin oxide)/TiO2/MAPbI3/wet hole transporting material (HTM) with additives and PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid))/indium tin oxide (ITO). The best FTO/TiO2/MAPbI3/P3HT with additives/PEDOT:PSS/ITO planar sandwich structured solar cells exhibited a 12.8% (deviation: 11.7% ± 0.74%) average power conversion efficiency (ηavg) but poor visible transmittance due to strong absorption by P3HT. Meanwhile, the semi-transparent FTO/TiO2/MAPbI3/PTAA with additives/PEDOT:PSS/ITO planar sandwich solar cells exhibited a 15.8% (deviation: 14.45% ± 0.76%) ηavg without significant J–V hysteresis with respect to the forward and reverse scan directions. The average visible transmittance (AVT) was controlled from 17.3% to 6.3% and the corresponding ηavg changed from 12.55% to 15.8%. The unsealed sandwich planar perovskite solar cells exhibited great air and humidity stability over 20 days due to the self-passivated device architecture of the sandwich type device.

A [2,2]paracyclophane triarylamine-based hole-transporting material for high performance perovskite solar cells

We report the development of a novel hole transporting material (HTM), PCP-TPA, based on [2,2]paracyclophane. In comparison to the well-known HTM, spiro-OMeTAD, PCP-TPA could be prepared using a simple synthesis and showed a higher hole mobility due to effective intermolecular aggregation in the film state. When used as a HTM in perovskite solar cells, the power conversion efficiency reached 17.6%. PCP-TPA will potentially replace spiro-OMeTAD and advance the development of cost-effective and practical perovskite solar cells.

Highly efficient CH3NH3PbI3−xClx mixed halide perovskite solar cells prepared by re-dissolution and crystal grain growth via spray coating

We fabricated highly efficient planar type CH3NH3PbI3−xClx (MAPbI3−xClx) mixed halide perovskite solar cells via spray coating with a controlled composition of the solvents. The cells had a power conversion efficiency of 17.8% (forward scan), 18.3% (reverse scan), and 16.08 ± 1.28% (average) for unit cells under 1 Sun conditions. We controlled the ratio of DMF (dimethylformamide), a quickly evaporating solvent, and GBL (γ-butyrolactone), a slowly evaporating solvent, to 10u2006:u20060, 9u2006:u20061, 8u2006:u20062, and 7u2006:u20063 (volu2006:u2006vol). We obtained the largest MAPbI3−xClx mixed halide perovskite crystal grains in the 8u2006:u20062 sample because the inward flux of the spray solution was balanced with the outward flux of the evaporating solvent. Consequently, the moistened underlying polycrystalline perovskite film with small crystal grains re-dissolved and merged into larger crystalline grains by re-crystallization. By controlling the re-dissolution and crystal grain growth of the MAPbI3−xClx mixed halide perovskite film via spray coating, we fabricated a sub-module (10 cm × 10 cm, active area = 40 cm2) with 10.5 V open circuit voltage, 84.15 mA short circuit current, 70.16% fill factor, and 15.5% power conversion efficiency under 1 Sun conditions.

CH3NH3PbI3 planar perovskite solar cells with antireflection and self-cleaning function layers

We report CH3NH3PbI3 planar perovskite solar cells with multifunctional inverted micro-pyramidal structured (IMPS) polydimethylsiloxane (PDMS) antireflection (AR) layers for enhancing the device efficiency. These IMPS-PDMS films were fabricated via a facile and cost-effective soft lithography using micro-pyramidal structured silicon (Si) master molds formed by alkaline anisotropic wet-etching treatment of (100)-oriented monocrystalline Si substrates. The IMPS-PDMS laminated on the bare glass (i.e., IMPS-PDMS/glass) exhibited a higher solar weighted transmittance (TSW) value of ∼95.2% (or the lowest solar weighted reflectance (RSW) of ∼4.7%) than those of the bare glass and flat-PDMS/glass, i.e., TSW/RSW ∼ 90.7/9.1 and 91.5/8.2%, respectively. Additionally, it showed a much higher average haze ratio (HA) value of ∼93.1% compared to the bare glass and flat-PDMS/glass (i.e., HA ∼ 1.6 and 2.8%, respectively). By employing the IMPS-PDMS onto the outer surface of CH3NH3PbI3 planar perovskite solar cells as an AR layer, an improved short-circuit current density (Jsc) value of 21.25 mA cm−2 was obtained, as compared to the reference device and the device with flat-PDMS (i.e., Jsc = 20.57 and 20.87 mA cm−2, respectively), while showing the almost same Voc and FF values as those of the reference device. As a result, the power conversion efficiency was improved from 17.17 and 17.42% for the reference and flat-PDMS devices, respectively, to 17.74% for the IMPS-PDMS device. Also, the fluorooctyltrichlorosilane-treated IMPS-PDMS surface revealed a superhydrophobic behavior with a water contact angle of ∼150° which is useful for self-cleaning applications in outdoor environments.

A discussion on the origin and solutions of hysteresis in perovskite hybrid solar cells

Although the record efficiencies of perovskite hybrid solar cells are gradually reaching the efficiency of crystalline Si solar cells, perovskite hybrid solar cells often exhibit significant current density–voltage (J–V) hysteresis with respect to the forward and reverse scan direction and scan rate. The origin of the J–V hysteresis of perovskite hybrid solar cells has not, to date, been clearly elucidated. Dielectric polarization by the ferroelectric properties of perovskite (i), the ionic motion/migration of perovskite materials (ii), and charge trapping and detrapping at trap sites by the unbalanced electron and hole flux (iii) are considered the possible origins of J–V hysteresis. Here, we reviewed the origin of the J–V hysteresis of perovskite solar cells from the above three points of view and we then suggest how one may reduce the J–V hysteresis with respect to the scan direction and scan rate.

PbS colloidal quantum-dot-sensitized inorganic-organic hybrid solar cells with radial-directional charge transport.

Colloidal quantum dots (CQDs) have been intensively studied owing to their unique optical and physical properties such as convenient electronic bandgap control by the quantum confinement effect, strong absorption over broad wavelength regions, an intrinsically large dipole moment, and multiple exciton generation by impact ionization. In particular, it is expected that the unique properties of CQDs will greatly improve solar cells because their solution processability at relatively lower processing temperatures can reduce the fabrication cost and yield flexible thin-film solar cells. Accordingly, intensive studies have been performed to develop efficient CQD solar cells with inorganic metal chalcogenides such as CdS(e), PbS(e), HgTe, and CuInTe(Se). Among them, near-infrared (NIR)-responsive PbS CQDs have been of great interest because PbS has a low bulk energy bandgap of ~0.4 eV and a large Bohr radius of 18 nm. Since Gr tzel et al. first reported dye-sensitized solar cells, these sensitized solar cells have been intensively studied over the past two decades in an effort to develop cost-effective solar cells. Sensitized solar cells are composed of an electron conductor, a sensitizer, and a hole conductor. This setup allows the generated electron–hole pairs to quickly separate into electron conductors and hole conductors. The probability of recombination is thus greatly reduced, even when relatively impure materials are used. However, the conventional Ru dyes and liquid electrolytes used in dye-sensitized solar cells might limit the ability to fabricate flexible optoelectronics because the weak absorption coefficient of Ru dyes requires a mesoporous TiO2 electrode over 10 mm thick to fully absorb the light. Further, the liquid electrolyte could potentially leak when subjected to bending. Therefore, it is desirable to develop an allsolid-state sensitized solar cell with a relatively thin photoelectrode. As part of an effort to develop all-solid-state inorganic CQDsensitized solar cells (SSCs), we previously demonstrated PbS CQD-SSCs with a device architecture of mesoporous TiO2/PbS CQDs and poly-3-hexylthiophene (P3HT) and spiro-MeOTAD [2,2’,7,7’-tetrakis(N,N-di-p-methoxyphenylamine)-9,9’-spirobifluorene] , which serve as organic hole-transporting materials (HTMs). From our previous studies, we found that the PbS CQDs can be more densely packed in the top section of a mesoporous TiO2 electrode, even though some PbS CQDs successfully infiltrate into the bottom section of the TiO2 electrode and the effectiveness of the organic HTMs is reduced by the infiltration of the HTMs into the narrow pores of the PbS CQDs deposited on the mesoporous TiO2. Therefore, we considered that a one-dimensional (1D) TiO2 electrode would provide sufficient pore space, enabling a good penetration of HTM into the surface of the PbS CQD/TiO2 electrode. Using a device architecture of 1D TiO2 nanorod electrode/PbS CQD/P3HT HTM, the generated charge carriers in the PbS CQDs could be transported in a radial direction, which is the shortest pathway to deliver the charge carriers into the electrode. Therefore, we could significantly improve the fill factor as compared to conventional mesoscopic TiO2 nanoparticle-based PbS CQD-SSCs. Scheme 1 shows an illustration of the PbS CQD-SSCs with radial-directional charge transport. We thought that the shortest pathway to extract the charge carriers generated in multistacked PbS CQDs was to use 1D TiO2 and separate the charge carriers in the radial direction. Holes can be efficiently transported to the Au counter electrode through the P3HT HTM and PEDOT:PSS hole-conducting layer and at the same time the electrons can be done as well. Upon illumination with solar light, the PbS CQDs generate electron–hole pairs and the generated electrons (holes) are injected into the TiO2 photoelectrode (P3HT HTM). When an n–p heterojunction is made by n-type TiO2 and p-type PbS CQDs stacked into multiple layers, the charge carriers have many opportunities to recom[a] S. Kim, J. H. Heo, Dr. J. H. Noh, Prof. S. I. Seok Solar Energy Materials Research Group Division of Advanced Materials Korea Research Institute of Chemical Technology 141 Gajeong-ro, Yuseong-gu Daejeon 305-600 (Korea) E-mail : seoksi@krict.re.kr [b] S. Kim, Prof. S.-W. Kim Department of Molecular Science and Technology Ajou University Suwon, 443-749 (Korea) E-mail : swkim@ajou.ac.kr [c] J. H. Heo, Prof. S. H. Im Department of Chemical Engineering College of Engineering Kyung Hee University 1 Seochon-dong, Giheung-gu Yongin-si, Gyeonggi-do 446-701 (Republic of Korea) E-mail : imromy@khu.ac.kr [d] Prof. S. I. Seok Department of Energy Science Sungkyunkwan University Suwon 440-746 (Korea) E-mail : seoksi@skku.edu [] Equal contributions. Supporting Information for this article is available on the WWW under http://dx.doi.org/10.1002/cphc.201300825.

Highly efficient solid-state mesoscopic PbS with embedded CuS quantum dot-sensitized solar cells

We synthesized a new type of PbS colloidal quantum dot (QDs) embedding CuS (PbS[CuS] QDs) by rapid injection of a sulfur precursor into a lead precursor solution followed by cation exchange of Pb with Cu ions. By the cation exchange reaction, the edge of PbS QDs was partially converted into CuS, which enhances the absorptivity of light and creates an additional absorption band in the near infrared (NIR) region due to the surface plasmon resonance (SPR) effect by the existence of vacancies in CuS. From the transient and static photoluminescence (PL) decay measurements, we found that the PL decay time of PbS[CuS] QDs was ∼2 fold longer than that of the PbS QDs and the PbS[CuS] QDs showed great PL quenching compared to the PbS QDs. Accordingly, the generated excitons in PbS/CuS QDs are more easily dissociated into free charge carriers than those in the PbS QDs. As a result, the mesoscopic PbS/CuS QD-sensitized solar cells constructed using FTO (F-doped SnO2)/bl-TiO2 (blocking TiO2)/mesoscopic TiO2/PbS/CuS CQDs/P3HT (poly-3-hexylthiophene)/Au showed 0.6 V open-circuit voltage (Voc), 20.7 mA cm−2 short-circuit current density (Jsc), 65% fill factor (FF), and 8.07% overall power conversion efficiency under 1 sun conditions (100 mW cm−2 AM 1.5G) due to the improved absorptivity and the reduced recombination of charge carriers.