Jun Ho Kim

Rapid thermal annealed WO3-doped In2O3 films for transparent electrodes in organic photovoltaics

We investigated the effect of rapid thermal annealing (RTA) on the electrical, optical, structural and surface properties of WO3-doped In2O3 (IWO) films for use in organic solar cells (OSCs). Increasing the RTA temperature led to significant decreases in resistivity and sheet resistance due to activation of the W dopants and the (2 2 2) preferred orientation of the IWO films. At the optimized RTA temperature of 500 °C, the IWO film had a sheet resistance of 21 Ω/square and an optical transmittance of 89.39%, which is comparable to conventional ITO electrodes. Due to the high mobility of 46 cm2 V−1 s−1, the IWO film showed a higher optical transmittance in the near infrared wavelength region even though it had a low resistivity of 4.34 × 10−4 Ω cm. Furthermore, the 500 °C annealed IWO film showed very smooth surface morphology due to its (2 2 2) preferred orientation. The performance (fill factor of 61.59%, short circuit current of 8.84 mA cm−2, open circuit voltage of 0.60 V and power conversion efficiency of 3.27%) of the OSC fabricated with the IWO electrode was nearly identical to that of the OSC with a reference ITO anode, indicating that the IWO anode is a promising high-mobility transparent electrode material to replace conventional ITO anodes for high-performance OSCs.

Highly Transparent and Low-Resistance Indium-Free ZnO/Ag/ZnO Multilayer Electrodes for Organic Photovoltaic Devices

We investigated the effect of ZnO layer thickness on the optical and electrical properties of ZnO/Ag/ZnO multilayer films deposited on glass substrates. The transmission window became wider and shifted toward the lower energy side with increasing ZnO thickness. The ZnO/Ag/ZnO (40 nm/18.8 nm/40 nm) multilayer sample showed transmittance of ~96% at 550nm. As the ZnO thickness was increased from 8 nm to 80 nm, the carrier concentration gradually decreased from 1.74 × 1022xa0cm−3 to 4.33xa0×xa01021xa0cm−3, while the charge mobility varied from 23.8xa0cm2/V-s to 24.8xa0cm2/V-s. With increasing ZnO thickness, the samples exhibited similar sheet resistances of 3.6xa0Ω/sq to 3.9xa0Ω/sq, but the resistivity increased by a factor of 4.58. The samples showed smooth surfaces with root-mean-square roughness in the range of 0.47xa0nm to 0.94xa0nm. Haacke’s figure of merit (FOM) was calculated for all the samples; the ZnO (40xa0nm)/Ag (18.8xa0nm)/ZnO (40xa0nm) multilayer produced the highest FOM of 148.9xa0×xa010−3xa0Ω−1.

Transparent Conductive ITO/Ag/ITO Electrode Deposited at Room Temperature for Organic Solar Cells

We investigated the optical and electrical properties of room-temperature-deposited indium-tin-oxide (ITO)/Ag (19xa0nm)/ITO multilayer films as a function of ITO layer thickness. The optical and electrical properties of the ITO/Ag/ITO films were compared with those of high-temperature-deposited ITO-only films for use as an anode in organic solar cells (OSCs). The ITO/Ag/ITO multilayer films had sheet resistances in the range 5.40–5.78xa0Ω/sq, while the ITO-only film showed 14.18xa0Ω/sq. The carrier concentration of the ITO/Ag/ITO films gradually decreased from 2.01xa0×xa01022 to 7.20xa0×xa01021xa0cm−3 as the ITO thickness increased from 17xa0nm to 83xa0nm. At 530xa0nm, the transmittance of the ITO/Ag/ITO (50xa0nm/19xa0nm/50xa0nm) films was ~90%, while that of the ITO-only film gave 96.5%. The multilayer film had a smooth surface with a root mean square (RMS) roughness of 0.49xa0nm. Poly (3-hexylthiophene) (P3HT):[6,6]-phenyl-C61 butyric acid methylester (PCBM) bulk heterojunction (BHJ)-based OSCs fabricated with the ITO/Ag/ITO (50xa0nm/19xa0nm/50xa0nm) film showed a power conversion efficiency (PCE) (2.84%) comparable to that of OSCs with a conventional ITO-only anode (3.48%).

Highly transparent Nb-doped indium oxide electrodes for organic solar cells

The authors investigated the characteristics of Nb-doped In2O3 (INbO) films prepared by co-sputtering of Nb2O5 and In2O3 for use in transparent anodes for organic solar cells (OSCs). To optimize the Nb dopant composition in the In2O3 matrix, the effect of the Nb doping power on the resistivity and transparency of the INbO films were examined. The electronic structure and microstructure of the INbO films were also investigated using synchrotron x-ray absorption spectroscopy and x-ray diffraction examinations in detail. At the optimized Nb co-sputtering power of 30u2009W, the INbO film exhibited a sheet resistance of 15u2009Ω/sq, and an optical transmittance of 86.04% at 550u2009nm, which are highly acceptable for the use as transparent electrodes in the fabrication of OSCs. More importantly, the comparable power conversion efficiency (3.34%) of the OSC with an INbO anode with that (3.31%) of an OSC with a commercial ITO anode indicates that INbO films are promising as a transparent electrode for high performance OSCs.

Formation of Flexible and Transparent Indium Gallium Zinc Oxide/Ag/Indium Gallium Zinc Oxide Multilayer Film

In this study, the electrical, optical, and bending characteristics of amorphous indium gallium zinc oxide (IGZO)/Ag/IGZO (39xa0nm/19xa0nm/39xa0nm) multilayer films deposited on polyethylene terephthalate (PET) substrate at room temperature were investigated and compared with those of Sn-doped indium oxide (ITO) (100xa0nm thick) films. At 500xa0nm the ITO film transmitted 91.3% and the IGZO/Ag/IGZO multilayer film transmitted 88.8%. The calculated transmittance spectrum of the multilayer film was similar to the experimental result. The ITO film and IGZO/Ag/IGZO multilayer film, respectively, showed carrier concentrations of 1.79xa0×xa01020 and 7.68xa0×xa01021xa0cm−3 and mobilities of 27.18xa0cm2/Vxa0s and 18.17xa0cm2/Vxa0s. The ITO film had a sheet resistance of 134.9xa0Ω/sq and the IGZO/Ag/IGZO multilayer film one of 5.09xa0Ω/sq. Haacke’s figure of merit (FOM) was calculated to be 1.94xa0×xa010−3 for the ITO film and 45.02xa0×xa010−3xa0Ω−1 for the IGZO/Ag/IGZO multilayer film. The resistance change of 100xa0nm-thick ITO film was unstable even after five cycles, while that of the IGZO/Ag/IGZO film was constant up to 1000 cycles.

Effects of rapid thermal annealing on electrical, optical, and structural properties of Ni-doped In2O3 anodes for bulk heterojunction organic solar cells

The authors investigated the effects of rapid thermal annealing (RTA) on the electrical, optical, and structural properties, and work functions of Ni-doped In2O3 (INO) anodes prepared by a DC/RF co-sputtering process for use in bulk heterojunction organic solar cells (OSCs). By RTA processing at 600u2009°C, the authors obtained the optimized INO anodes with a sheet resistance of 28 Ω/sq, an optical transmittance of 82.93%, and a work function of 5.02u2009eV, which are acceptable in OSC fabrication. In particular, the 600u2009°C annealed INO anode showed much higher optical transmittance in the near infrared wavelength region than the conventional ITO film, even though it had a low resistivity of 5.66u2009×u200910−4 Ω cm. The OSC fabricated on the annealed INO anode showed a higher power convention efficiency of 2.65% than the OSC with as-deposited INO anodes (2.19%) because the fill factors of the OSC are critically dependent on the sheet resistance of the anode.

Improving the thermal stability of nickel monosilicide thin films by combining annealing with the use of an interlayer and a capping layer

The authors investigated the effects of preannealing a 2-nm-thick Pd interlayer and a 20-nm-thick TiN capping layer on the electrical and thermal stability of nickel silicides as a function of the annealing temperature. The preannealed samples (prepoly-Si) produce lower sheet resistances compared to the samples without preannealing. For the preannealed samples, NiSi remains stable up to 600u2009°C. Transmission electron microscopy results show that the preannealed samples have a higher resistance against layer inversion. The addition of a Pd interlayer at the Ni film/prepoly-Si interface increases the formation temperature of NiSi2 to 900u2009°C. The use of the capping layer on the Pd-interlayered prepoly-Si samples improves the electrical and morphological stabilities of NiSi. The possible mechanisms for the preannealing and interlayer-induced improvement of the thermal stabilities of the Ni-silicide samples are discussed in terms of grain growth and simple thermodynamic relations.

Electron Transport Layer-Free Inverted Organic Solar Cells Fabricated with Highly Transparent Low-Resistance Indium Gallium Zinc Oxide/Ag/Indium Gallium Zinc Oxide Multilayer Electrode

Inverted organic solar cells (OSCs) have been fabricated with conventional Sn-doped indium oxide (ITO) and amorphous indium gallium zinc oxide (a-IGZO)/Ag/a-IGZO (39xa0nm/19xa0nm/39xa0nm) (a-IAI) electrodes and their electrical characteristics characterized. The ITO and optimized a-IAI electrodes showed high transmittance of 96% and 88% at 500xa0nm, respectively. The carrier concentration and sheet resistance of the ITO and a-IAI films were 8.46xa0×xa01020xa0cm−3 and 7.96xa0×xa01021xa0cm−3 and 14.18xa0Ω/sq and 4.24xa0Ω/sq, respectively. Electron transport layer (ETL)-free OSCs with the a-IAI electrode exhibited power conversion efficiency (PCE) of 2.66%, similar to that of ZnO ETL-based OSCs with ITO electrode (3.27%). However, the ETL-free OSCs with the a-IAI electrode showed much higher PCE than the ETL-free OSCs with the ITO electrode (0.84%). Ultraviolet photoelectron spectroscopy results showed that the work function of the a-IAI electrode was 4.15xa0eV. This improved performance was attributed to the various roles of the a-IAI electrode, e.g., as an effective ETL and a hole blocking layer.