Yong Chan Choi

Daegu Gyeongbuk Institute of Science and Technology | DGIST · Division of Energy Technology

The hole transport layer (HTL) plays a key role in inverted perovskite solar cells (PSCs), and nickel oxide has been widely adopted for HTL. However, a conventional solution‐processed bottom‐up approach for NiO x (S‐NiO) HTL fabrication shows several drawbacks, such as poor coverage, irregular film thickness, numerous defect sites, and inefficient...

Solar cell technology is an effective solution for addressing climate change and the energy crisis. Therefore, many researchers have investigated various solar cell absorbers that convert sunlight into electric energy. Among the different materials researched, heavy pnictogen chalcohalides comprising heavy pnictogen cations, such as Bi3+ and Sb3+,...

Ternary chalcohalides are promising lead-free photovoltaic materials with excellent optoelectronic properties. We propose a simple one-step solution-phase precursor-engineering method for antimony selenoiodide (SbSeI) film fabrication. SbSeI films were fabricated by spin-coating the precursor solution, and heating. Various precursor solutions were...

Despite their comparable performance to commercial solar systems, lead-based perovskite (Pb-perovskite) solar cells exhibit limitations including Pb toxicity and instability for industrial applications. To address these issues, two types of Pb-free materials have been proposed as alternatives to Pb-perovskite: perovskite-based and non-perovskite-ba...

Pb-based hybrid perovskite solar cells, despite their advantages, face challenges in commercialization. In recent years, Bi-based chalcohalides are being considered as potential alternative candidates, however, their current device efficiency remains unsatisfactory. Herein, a two-step solution method is developed and applied to the fabrication of B...

Tin sulfide (SnS) is one of the most promising solar cell materials, as it is abundant, environment friendly, available at low cost, and offers long‐term stability. However, the highest efficiency of the SnS solar cell reported so far remains at 4.36% even using the expensive atomic layer deposition process. This study reports on the fabrication of...

A 4,4′,4″-tris[phenyl(m-tolyl)amino]triphenylamine (m-MTDATA) was applied as an additive to hole-transporting poly(3-hexylthiophene) [P3HT] layers in perovskite solar cells. The incorporation of 0.5 wt% m-MTDATA to the P3HT layer led to an increased power conversion efficiency of 9.53%, due to an enhancement in the short circuit current, open-circu...

Plenty of chalcogenide families with tremendous potential for functional applications remain unexplored due to the limi-tations of conventional synthesis methods. However, cation exchange reactions in colloidal synthesis offer an alternative way to overcome these limitations and provide a route to synthesize pure phases and morphologies that otherw...

We report a simple solution processing method for fabricating low-temperature SbSI solar cells. The method consists of two steps: the formation of amorphous Sb2S3 and its transformation to SbSI. A pure SbSI phase with a high crystallinity was obtained at a low temperature of 200 °C. In addition, the SbSI morphology was controlled by tuning the inpu...

Sb2S3 is considered as one of the emerging light absorbers that can be applied to next-generation solar cells because of its unique optical and electrical properties. Recently, we demonstrated its potential as next-generation solar cells by achieving a high photovoltaic efficiency of > 6% in Sb2S3-sensitized solar cells using a simple thiourea (TU)...

Although antimony sulfoiodide (SbSI) exhibits very interesting properties including high photoconductivity, ferroelectricity, and piezoelectricity, it is not applied to solar cells. Meanwhile, SbSI is predominantly prepared as a powder using a high-temperature, high-pressure system. Herein, the fabrication of solar cells utilizing SbSI as light har...

Herein, we report on the systematic engineering of the interface between the titanium oxide (TiO2) photoelectrode and the antimony sulfide (Sb2S3) absorber layer in planar Sb2S3 solar cells, which was much unexplored, on the photovoltaic performance. Due to simple spin-coating process for the preparation of TiO2 and Sb2S3 layers, it was possible to...

We develop antisolvent-assisted powder engineering for the controlled growth of hybrid inorganic-organic CH3NH3PbI3 (MAPbI3) perovskite thin films. The powders, which are used as the precursors for solution processing, are synthesized by pouring a MAPbI3 precursor solution into various antisolvents, such as dichloromethane, chloroform, diethyl ethe...

High-quality CH3NH3PbI3 (MAPbI3) crystalline powders were synthesized from a dispersion of MAPbI3 solution in an antisolvent of dichloromethane. They were used as starting chemicals for precursor solutions. The PbI2-DMF(N,N-dimethyformamide)-, perovskite-, and PbI2-MAI(methylammonium iodide)-DMF-dominant phases were preferentially formed under cond...

In this work, we investigated the effects of the pyrolysis temperature on the structural, Raman, and infrared properties of PbTiO3 nanotubes (PTO-NTs). The PTO-NTs were synthesized by spin coating a sol-gel solution on porous anodic alumina membranes, followed by the pyrolysis step at 400 − 600 ℃. Then, PTO-NTs were finally crystallized at 600 − 70...

Sb2S3 sensitized solar cells are a promising alternative to devices employing organic dyes. The manufacture of Sb2S3 absorber layers is however slow and cumbersome. Here, we report the modified aqueous chemical bath synthesis of Sb2S3 absorber layers for sensitized solar cells. Our method is based on the hydrolysis of Sb2S3 to complex antimony ions...

To replace the conventional chemical bath deposition method, which is time-consuming and has a high impurity level, a chemical single-step deposition process employing a S/Sb ratio-controlled SbCl3-thiourea complex solution is introduced to load Sb2S3 into a mesoporous TiO2 electrode. This technique enables the fabrication of efficient and reproduc...

The device performance of sensitizer-architecture solar cells based on a CuSbS2 light sensitizer is presented. The device consists of F-doped SnO2 substrate/TiO2 blocking layer/mesoporous TiO2/CuSbS2/hole-transporting material/Au electrode. The CuSbS2 was deposited by repeated cycles of spin coating of a Cu-Sb-thiourea complex solution and thermal...

We report the phase evolution of Pb(Zr0.52Ti0.48)O3 nanotubes (PZT-NTs), from the pyrochlore to perovskite phase, with an outer diameter of about 420 nm and a wall thickness of about 10 nm. The PZT-NTs were fabricated in pores of porous anodic alumina membrane (PAM) using a spin coating of PZT sol–gel solution and subsequent annealing at 500–700 °C...

The light-harvesting Sb2S3 surface on mesoporous-TiO2 in inorganic-organic heterojunction solar cells is sulfurized with thioacetamide (TA). The photovoltaic performances are compared before and after TA treatment, and the state of the Sb2S3 is investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and deep-level transient spectroscop...

A Sb2(S1-x/Sex)3 graded-composition is obtained by a sequential deposition of Sb 2S3 and Sb2Se3 onto a mesoporous TiO2 photoelectrode followed by thermal annealing at 300 C. The compositional graded-solar cells exhibit a greatly enhanced performance compared to pristine Sb2S3-sensitized or Sb2Se 3-sensitized solar cells. The best performing cell, d...

The photovoltaic performance of Sb2 Se3 -sensitized heterojunction solar cells, which were fabricated by a simple deposition of Sb2 Se3 on mesoporous TiO2 by an approach that features multiple cycles of spin coating with a single-source precursor solution and thermal decomposition, is reported. Poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,...

We report on the strong pore-size-dependent optical properties of porous alumina membranes (PAMs) by using the photoluminescence and the optical spectroscopic techniques. The pore diameters of our PAMs varied from 60 to 420 nm. All samples showed a sizable violet/blue emission with a strong temperature dependence. We found that the peak position of...

For using 2,2′,7,7′-tetrakis(N,N′-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD) as a hole conductor in solar cells, it is necessary to improve its charge-transport properties through electrochemical doping. With the aim of fabricating efficient mesoscopic TiO2/CH3NH3PbI3 heterojunction solar cells, we used tris[2-(1H-pyrazol-1-yl)-4-...

We investigated the visible emission property of ultrathin-walled Pb(Zr,Ti)O3 (PZT) nanotubes (NTs) with various diameters. The PZTNTs were synthesized using the sol-gel templatedirected method with a spin-coating process. The photoluminescence (PL) spectra were measured by using the 325nm photo-excitation as a function of temperature. We observed...

We report the effects of wall-thickness on the morphology and structure of PbTiO3 nanotubes (PTO-NTs). The PTO-NTs were fabricated via template-directed growth in conjunction with sol-gel process and spin-coating technique. Wall-thickness was increased from 10 to 70 nm by repeating the process of ‘spin-coating and subsequent pyrolysis’. X-ray diffr...

We investigated the effect of etching time on the bottom surface morphologies of ultrathin porous alumina membranes (UT-PAMs) anodized in oxalic and phosphoric acid. The morphology of the bottom surface clearly changed and a unique surface undulation was observed during the etching process. Such an undulation regarding the bottom surface is attribu...

A porous anodic alumina (PAA) template was manufactured to investigate the pore effect on the formation of lubricating layers. A PAA template with 260 nm pores was manufactured by two-step anodization using phosphoric acid. A sliding wear test was carried out using a ball-on-disk tester. Due to the pore effect, an aluminum hydroxide film; i.e., the...

We report the effects of adsorbates on the Raman spectra of Pb(Zr0.4Ti0.6)O3 nanotubes (PZT-NTs). PZT-NTs with adsorbates were prepared by exposing PZT-NTs to air for 1 day. We found that the presence of surface adsorbates can cause an intense and broad Raman background that hinders the observation of the Raman vibrational modes of the PZT-NTs. Thi...

The nano-ferroelectrics community has taken a keen interest over the past 65 years in achieving the toroidal (circular) ordering of electric domains. Understanding the behavior of vortex ferroelectric domain states remains an unresolved issue because electric polarization density interactions contribute significantly to large extrinsic effects if t...

We describe variations in the structure and formation mechanism of alumina nanowires (ANWs) formed from porous anodic alumina (PAA) membranes, depending on the com-position of the etching solution. Two types of ANWs were synthesized by etching PAA membranes in etching solutions containing H 3 PO 4 or NaOH. Not only did the ANW for-mation mechanism...

Lead zirconate titanate (PZT) nanowires are successfully synthesized by a spin coating of sol-gel solution on a highly ordered porous alumina membrane (PAM). Field emission scanning electron microscope images show that PZT nanowires are well packed inside the nanochannels of the PAM. A selected area electron diffraction pattern reveals that they ar...

We present a systematic analysis of the nanotube-synthesis method of template-directed growth in conjunction with the sol-gel process and a spin-coating technique (TSS). Advantages and disadvantages of the TSS method are described.. The method is a simple, highly reproducible, and time-saving method to prepare multi-functional complex metal-oxide n...

Porous anodic alumina (PAA) templates having three kinds of nanometer pores were manufactured to investigate the effects of pores on an anodized aluminum surface as lubricant reservoir. Ball-on-disk wear tests of the PAA templates were carried out in the three types of lubrication conditions. The PAA templates submerged under water for 30 min showe...

We investigate the nanopore changes near domain boundaries during the nanopore growth in porous anodic alumina (PAA) to understand the domain growth behavior with the anodization time. In order to observe the pore changes with the time, we analyze cleavage planes of PAA according to the nanopore length using a field emission scanning electron micro...

Double-shelled nanotubes composed of inner shell Pb(Zr0.52Ti0.48)O3 (PZT) and outer shell TiO2 are successfully fabricated by a spin coating of each sol-gel solution on porous anodic alumina template. Field emission transmission electron microscopy images show that they have a ~ 10 nm wall thickness. The selected area electron diffraction patterns...

We report for the first time the self-assembled growth of nanocomposites of 'TiO2 nanopillars on Pb(Zr0.52Ti0.48)O3 (PZT) thin films' using a modified sol–gel processing. Both TiO2 nanopillars and PZT thin films are simultaneously formed during the post-annealing process. The growth behaviours of TiO2 nanopillars are controlled by adjusting the Ti...

We report the first unambiguous ferroelectric properties of ultra-thin-walled Pb(Zr,Ti)O 3 (PZT) nanotube arrays, each with 5 nm thick walls and outer diameters of 50 nm. Ferroelectric switching behavior with well-saturated hysteresis loops is observed in these ferroelectric PZT nanotubes with P r and E c values of about 1.5 microC cm (-2) and 86 k...

We report a synthesis and a structural characterization of crystalline metal-oxide PbO2 (lead di-oxide) nanowires. Single crystalline PbO2 nanowires with an average diameter of about 42 nm were successfully synthesized by a spin-coating process of putting a lead oxide sol-gel solution into a nano-porous anodic alumina membrane (nPAAM). The high-res...

We report the growth characteristics of porous alumina templates (PATs) with various shaped nanopores, including straight, step-shaped, and Y-branched nanopores. Self-organization of a two-dimensional array of nanopores, which was formed by anodic oxidation of aluminum, was investigated quantitatively by using field emission scanning electron micro...

We report a template-directed growth of Pb(Zrx,Ti 1-x)O3 (PZT) nanotubes in conjunction with sol-gel process and spin coating technique and its shape modification with an electron-beam (e-beam) irradiation. Field emission scanning electron microscope (FESEM) and field emission transmission electron microscope (FETEM) images show that PZT nanotubes...

We report a template-directed growth of Pb(Zrx,Ti1 − x)O3 (PZT) nanotubes in conjunction with sol-gel process and spin coating technique. Field emission scanning electron microscope (FESEM) images show that PZT nanotubes are well packed inside the pore of a porous alumina membrane (PAM). A Field emission transmission electron microscope (FETEM) ima...

Self-organization of a two-dimensional array of nanopores, which was formed by anodic oxidation of aluminum, was investigated quantitatively using scanning electron microscopy (SEM) images and their fast Fourier transformation analysis. The highly ordered array of nanopores with diameters of ~60 nm was obtained by two-step anodization at an anodizi...

We report the structure of alumina nanowires (ANWs) synthesized by the chemical etching of an anodic alumina membrane (AAM). The AAM was prepared by the two-step anodization method followed by the lift-off process. The field emission transmission electron microscopy analyses showed that the AAM consists of a gel-like structure, an outer layer, and...

We report alumina-membrane-based growth of functional PbO2 and Pb(Zr,Ti)O3 metal-oxide nanowires by combination of sol-gel processing and spin coating. Nanowires with a uniform diameter throughout the entire length and a relatively smooth surface are synthesized by the method. Fabricated PbO2 nanowires show a single crystalline structure with diame...

We report the template-based formation of functional complex metal-oxide nanostructures by a combination of sol–gel processing and spin coating. This method employs the spin-coating of a sol–gel solution into an anodic aluminum oxide membrane (SSAM). Various metal-oxide nanowires and nanotubes with a high aspect-ratio were prepared. The aspect-rati...

We report the first direct observation of the formation process of an alumina nanowire (ANW) array from a porous anodic alumina (PAA) membrane employing a simple droplet etching method, not a general immersion etching method, using field emission scanning electron spectroscopy (FESEM). The PAA membrane is prepared by the two-step anodization method...