Dasom Park

PbS/ZnO Heterojunction Colloidal Quantum Dot Photovoltaic Devices by a Room Temperature Air-Spray Method

Colloidal quantum-dot-based photovoltaic devices (CQDPVs) were fabricated at room temperature in air atmosphere via a spraying technique. Lead sulfide colloidal quantum dots (CQDs) were utilized for this process and various fabrication conditions such as the spraying pressure, types of ligand molecules, duration of ligand exchange, and the band-gap of the CQDs were investigated in order to optimize the device performance. The power conversion efficiency reached 4.00% (VOC of 0.57V, JSC of 11.79 mA·cm-2, and FF of 0.60) when ~145 nm thick sprayed CQD layers were utilized; this value is comparable to that achieved with the conventional spin-coated devices. The generality of the conditions used for fabrication of the sprayed CQDPVs was demonstrated in the fabrication of various CQDs having different band-gaps (1.34-1.61 eV). This technique provides an avenue for the application of a high-throughput process for CQDPV fabrication. Because the materials used herein for device fabrication are not completely optimized, there is further scope for improving device performance.

Efficient solvent-assisted external treatment for planar heterojunction small-molecule organic solar cells

We developed a novel solvent-assisted treatment (SAT) technique to modify the nanomorphology of the planar heterojunction (PHJ) bilayer active layers (ZnPc/C60) of organic photovoltaics (OPVs). The SAT technique uses organic solvent vapors under reduced pressures, which partially dissolves one component (the donor molecule, ZnPc, in this study) of PHJ layers prepared by vacuum deposition. Because of the partial mixing of the two layers, the PHJ layers develop a bulk heterojunction (BHJ)-like intermixed morphology. The performance of the resulting OPVs is considerably improved because of (i) the increased interfacial area of ZnPc/C60, (ii) the healing of the intrinsic micropores within the active layers, which originate from the deposition process, and (iii) enhanced light absorption due to the rearrangement of ZnPc molecules. After the SAT, the power conversion efficiency (PCE) of OPVs improved more than three-fold (2.58%), with an open-circuit voltage (VOC) of 0.61 V, a short-circuit current (JSC) of 7.50 mA cm−2, and a fill factor (FF) of 0.56, as compared to that of the as-prepared PHJ-OPVs (PCE = 0.83%, with VOC = 0.38 V, JSC = 5.3 mA cm−2, and FF = 0.42). Our unique SAT technique provides an alternative route for controlling the nanomorphology of organic thin films by vacuum deposition, which may be very difficult to achieve using more conventional methods.

PVP-assisted Synthesis of TiO₂ Nanospheres and their Application to the Preparation of Superhydrophobic Surfaces

Enhancement of the surface hydrophobicity of polydimethylsiloxane (PDMS) thin films deposited on substrates covered with titanium dioxide (TiO₂) nanospheres was studied. First, a low-temperature solution-phase method using polyvinylpyrrolidone (PVP) as a surface capping agent and a water/dimethylformamide (DMF) mixture as the reaction medium was used to synthesize monodisperse TiO₂ nanospheres. It was possible to easily control hydrolysis rate of the Ti-precursors and the size of the synthesized nanospheres by varying the amount of PVP and the volume ratio of the solvent mixture. Spray coating of the synthesized TiO₂ nanospheres under the PDMS film increased the water contact angle of the film surface to 150.3°. This simple treatment can modify the surface morphology at a nanometer scale without any long or complicated nanoprocess; hence, the surface enters the superhydrophobic Cassie-Baxter regime.