Kwang Sun Ji

Microstructure and Light-Scattering Properties of ZnO:Al Films Prepared Using a Two-Step Process through the Control of Oxygen Pressure

ZnO:Al films were prepared using a two-step process involving the control of oxygen pressure. The seed layers were deposited under various Ar to oxygen pressure ratios, and the bulk layers were prepared under pure Ar. The growth mode was systematically examined and clearly different microstructures were shown according to the deposition condition of the seed layer. With increase of oxygen pressure, the crystallinity and the degree of (002) texturing increased. The haze values of etched films also increased with increasing oxygen pressure, which was explained by the grain-structure of as-deposited films.

The Emitter Having Microcrystalline Surface in Silicon Heterojunction Interdigitated Back Contact Solar Cells

In producing the Si heterojunction interdigitated backcontact solar cells, we investigated the feasibility of applying amorphous Si emitter having considerable crystalline Si phase at the facing to transparent conducting oxide (TCO) layer. Prior to evaluating electrical property, we characterized material nature of hydrogenated microcrystalline p-type silicon (µc-p-Si:H) as crystallized fraction, surface morphology, bonding kinds in thin films and then surface passivation quality finally. The diode and interface contact characteristics were induced by the simple test device and then current–voltage (I–V) curve showed more linearity in µc/hydrogenated amorphous silicon (a-Si:H) emitter case. We fabricated heterojunction back contact (HBC) solar cells using p/n interdigitated structure and acquired the 23.4% efficiency in cell size with performance parameters as open-circuit voltage (Voc) 723 mV, short-circuit current density (Jsc) 41.8 mA/cm2, fill factor (FF) 0.774, in the cell size (at 2×2 cm2).

Enhancement of Crystallinity in ZnO:Al Films Using a Two-Step Process Involving the Control of the Oxygen Pressure

The ZnO:Al films were prepared using a two-step process through the control of oxygen pressure by DC-pulsed magnetron sputtering. The seed layers were prepared with various Ar to oxygen pressure, and the bulk layers were deposited under pure Ar. At the seed-layer condition of Ar/O2 = 24/1 (Ar rich), the seed layer showed grains that led to the formation of hillock, and the grains of seed layer were seem to act as nucleation sites for columnar growth of bulk layer. While, at the seed-layer condition of Ar/O2 =4/1 (oxygen rich), grains show large lateral growth with a nonuniform distribution, and a number of dislocations are shown in grains. As oxygen pressure during the deposition of seed layer increased, the decrease of local strain (or the increase of crystallinity) was observed. The etched surface showed the crater-like structure and the abrupt morphology change appeared at high oxygen pressure, which was likely due to nonuniform grain structure and/or the decrease in the number of chemical attack sites by the drastic decrease of grain boundary. The haze values increased with increasing oxygen pressure, which was explained by the change of crater size, as shown in the AFM image.

Enhancement of crystallinity in ZnO:Al films using a two-step process involving the control of the oxygen pressure

The ZnO:Al films were prepared using a two-step process through the control of oxygen pressure by DC-pulsed magnetron sputtering. The seed layers were prepared with various Ar to oxygen pressure, and the bulk layers were deposited under pure Ar. At the seed-layer condition of Ar/O 2 = 24/1 (Ar rich), the seed layer showed grains that led to the formation of hillock, and the grains of seed layer were seem to act as nucleation sites for columnar growth of bulk layer. While, at the seed-layer condition of Ar/O 2 =4/1 (oxygen rich), grains show large lateral growth with a nonuniform distribution, and a number of dislocations are shown in grains. As oxygen pressure during the deposition of seed layer increased, the decrease of local strain (or the increase of crystallinity) was observed. The etched surface showed the crater-like structure and the abrupt morphology change appeared at high oxygen pressure, which was likely due to nonuniform grain structure and/or the decrease in the number of chemical attack sites by the drastic decrease of grain boundary. The haze values increased with increasing oxygen pressure, which was explained by the change of crater size, as shown in the AFM image.

Surface passivation properties of boron and phosphor-doped a-Si:H films with multi-step deposition for si heterojunction solar cells

Heterojunction, such as the crystalline silicon(c-Si)/hydrogenated amorphous silicon (a-Si:H), forms a high quality passivation properties and developed for a very low recombination contact for photovoltaic devices. As low as doppant concentration (like un-doped or intrinsic), the defect density is decreased and its passivation properties is enhanced, however, in case of emitter or BSF, the low doppant concentration can cause higher contact resistance with TCO or metal electrode simultaneously, so the doping concentration limited by this reason. In this work, we studied the method avoiding doppant concentration limitation in p and n type a-Si:H films with multi layer deposition. The doped p and n type a-Si:H films were divided as two layers, passivation and contacting, through in-situ multistep deposition with different doppant flow rate. The passivation properties of multistep deposited p type a-Si:H films revealed that there were no degradation of lifetime(teff) and implied Voc as increasing doppant concentration, differ from n type case, and showed enhanced open circuit voltage and quantum efficiency at short wavelength.