Jin Sun Yoo

Retarding charge recombination in perovskite solar cells using ultrathin MgO-coated TiO2 nanoparticulate films

MgO-coated TiO2 nanoparticle (NP)-based electron collecting layers were fabricated to prevent charge recombination at the methylamine lead iodide/TiO2 interface in perovskite solar cells. The open circuit voltage (Voc) and fill factor (ff) of perovskite solar cells based on MgO-coated TiO2 charge collectors were 0.89 V and 71.2%, respectively. These values were 4.7% and 6.1% higher than the pure TiO2 based perovskite solar cells. Transient photovoltage decay data exhibited recombination times for MgO-coated TiO2 NP-based perovskite solar cells about three times longer than those of TiO2 NP based solar cells. The longer recombination time was responsible for enhancing the Voc and ff of MgO-coated TiO2 NP-based perovskite solar cells. By employing a MgO nanolayer, we observed that the power conversion efficiency (PCE) was increased from 11.4% to 12.7%, demonstrating that MgO ultrathin nanolayers are able to efficiently retard charge recombination in perovskite solar cells.

Long-term stable stacked CsPbBr3 quantum dot films for highly efficient white light generation in LEDs

We report highly efficient ethyl cellulose with CsPbBr3 perovskite QD films for white light generation in LED application. Ethyl cellulose with CsPbBr3 quantum dots is applied with Sr2Si5N8 : Eu2+ red phosphor on an InGaN blue chip, achieving a highly efficient luminous efficacy of 67.93 lm W-1 under 20 mA current.

Highly Stable Perovskite Solar Cells in Humid and Hot Environment

An organic–inorganic perovskite solar cell (PSC) is a very promising candidate for a next-generation photovoltaic system. For the last three years, the power conversion efficiency (PCE) of PSCs has been dramatically improved from 9.7% to 22.1%; however, a poor long-term stability still limits the commercialization of PSCs. In this study, we explore the effect of poly(methyl methacrylate) (PMMA)/reduced graphene oxide (rGO) composite (PRC) passivation layer on the chemical and thermal stability of PSCs. The PRC passivation layer shows superior protection performance due to improved hydrophobicity and increased complexity of the O2 or H2O diffusion pathway. Moreover, the excellent thermal conductivity of rGO facilitates heat dissipation through the PRC layer. When the PRC layer is coated, the aging of PSCs is significantly prevented even under extreme conditions of humidity (>75%) and temperature (∼85 °C). Consequently, the PCE of PRC-passivated PSCs exhibits a negligible change in air, temperature of 35 °C, and humidity of 40% for 1000 h. Our study offers a simple and robust way to fabricate long-term stable and highly efficient PSCs, thus providing a path to PSC commercialization.

A highly efficient and stable green-emitting mesoporous silica (MP)–(Cs0.4Rb0.6)PbBr3 perovskite composite for application in optoelectronic devices

We have, for the first time, reported a highly efficient MP–(Cs0.4Rb0.6)PbBr3 luminescent material for application in optoelectronic devices. MP–(Cs0.4Rb0.6)PbBr3 with red-emitting Sr2Si5N8:Eu2+ phosphor is applied to an InGaN blue chip and compared with green-emitting (Cs0.4Rb0.6)PbBr3 perovskite nanocrystals (NCs). MP–(Cs0.4Rb0.6)PbBr3 achieves a conversion efficiency of 80.9 lm W−1 under a forward-bias current of 150 mA. We propose MP–(Cs0.4Rb0.6)PbBr3 as a promising green-emitting material that can replace the conventional inorganic phosphor.

Innovatively Continuous Mass Production Couette-taylor Flow: Pure Inorganic Green-Emitting Cs 4 PbBr 6 Perovskite Microcrystal for display technology

We report for the first time the mass production of Cs4PbBr6 perovskite microcrystal with a Couette-Taylor flow reactor in order to enhance the efficiency of the synthesis reaction. We obtained a pure Cs4PbBr6 perovskite solid within 3 hrs that then realized a high photoluminescence quantum yield (PLQY) of 46%. Furthermore, the Cs4PbBr6 perovskite microcrystal is applied with red emitting K2SiF6 phosphor on a blue-emitting InGaN chip, achieving a high-performance luminescence characteristics of 9.79 lm/W, external quantum efficiency (EQE) of 2.9%, and correlated color temperature (CCT) of 2976 K; therefore, this perovskite is expected to be a promising candidate material for applications in optoelectronic devices.

Dual function of a high-contrast hydrophobic–hydrophilic coating for enhanced stability of perovskite solar cells in extremely humid environments

In spite of a continuous increase in their power conversion efficiency (PCE) and an economically viable fabrication process, organic–inorganic perovskite solar cells (PSCs) pose a significant problem when used in practical applications: They show fast degradation of the PCE when exposed to very humid environments. In this study, the stability of PSCs under very humid conditions is greatly enhanced by coating the surface of the PSC devices with a multi-layer film consisting of ultrahydrophobic and relatively hydrophilic layers. A hydrophobic composite of poly(methyl methacrylate) (PMMA), polyurethane (PU), and SiO2 nanoparticles successfully retards the water molecules from very humid surroundings. Also, the hydrophilic layer with moderately PMMA captures the residual moisture within the perovskite layer; subsequently, the perovskite layer recovers. This dual function of the coating film keeps the PCE of PSCs at 17.3% for 180 min when exposed to over 95% humidity.