Jaran Sritharathikhun

Optimization of Amorphous Silicon Oxide Buffer Layer for High-Efficiency p-Type Hydrogenated Microcrystalline Silicon Oxide/n-Type Crystalline Silicon Heterojunction Solar Cells

Intrinsic hydrogenated amorphous silicon oxide (i-a-SiO:H) films deposited by very high frequency plasma-enhanced chemical vapor deposition (60 MHz VHF-PECVD) at a low substrate temperature of approximately 200 °C were used as a front buffer layer in p-type hydrogenated microcrystalline silicon oxide/n-type crystalline silicon (p-µc-SiO:H/n-c-Si) heterojunction solar cells. We found that the oxygen concentration in the i-a-SiO:H buffer layer strongly affected the solar cell performance and that the short wavelength response in quantum efficiency (QE) was improved by oxygen addition. Employing a p-µc-SiO:H/i-a-SiO:H/n-Si [Czochralski (CZ), 200 µm, (100)]/i-a-Si:H/n-a-Si:H/Ag/Al configuration, we achieved an efficiency of 17.9% with Voc of 671 mV.

Surface Passivation of Crystalline and Polycrystalline Silicon Using Hydrogenated Amorphous Silicon Oxide Film

Excellent passivation properties of hydrogenated amorphous silicon oxide (a-SiOx:H) prepared by very high frequency plasma-enhanced chemical vapor deposition (VHF PECVD) at a low substrate temperature (170 °C) on crystalline and polycrystalline silicon (Si) wafers are reported. Films were characterized by ellipsometry, Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible (UV–vis) spectrophotometry, and dark-conductivity and photoconductivity measurements. A comparison of the results with those for different passivation layers such as hydrogenated amorphous silicon carbon nitride (a-SiCxNy:H), hydrogenated amorphous silicon nitride (a-SiNx:H), and hydrogenated amorphous silicon (a-Si:H) reveals their superiority as an excellent passivation layer for p-type crystalline Si as well as polycrystalline Si. A maximum effective lifetime of 400 µs was measured for 1–10 Ω cm, 380-µm-thick p-type c-Si using a micro-photocurrent decay (µ-PCD) system. Fixed charge density (Qf) was estimated by high-frequency (1 MHz) capacitance–voltage measurement using a metal–insulator–silicon structure (CV-MIS). The effect of annealing temperature on surface passivation in a nitrogen atmosphere was also studied.

Fabrication of microcrystalline cubic silicon carbide/crystalline silicon heterojunction solar cell by hot wire chemical vapor deposition

The n-type microcrystalline cubic silicon carbide (µc-3C–SiC:H) films were deposited by hot wire chemical vapor deposition (HWCVD) at a low substrate temperature (~300 °C). Heterojunction silicon based photovoltaic devices were fabricated by depositing wide band gap n-type µc-3C–SiC thin films on p-type Si wafers, whose thickness and resistivity were 200 µm and 1–10 Ω cm, respectively. The silicon wafers were textured using alkaline etchant prior to the device fabrication. The photovoltaic parameters of a typical device were found to be Voc=560 mV, Jsc=35.0 mA/cm2, fill factor (F.F.) = 0.724, and η=14.20%. Numerical analysis was performed using automat for simulation of hetero structures (AFORS-HET), a one-dimensional device simulators to determine the probable cause of the changes in device parameters before and after the ageing of the filament.

Optimization of p-Type Hydrogenated Microcrystalline Silicon Oxide Window Layer for High-Efficiency Crystalline Silicon Heterojunction Solar Cells

Wide-gap, high-conductivity p-type hydrogenated microcrystalline silicon oxide (p-µc-SiO:H) films deposited by very high frequency plasma-enhanced chemical vapor deposition (60 MHz VHF-PECVD) at a low substrate temperature of approximately [200 °C] were used as window layers in n-type crystalline silicon (n-c-Si) heterojunction (HJ) solar cells. We investigated the effect of p-µc-SiO:H window layer thickness on HJ solar cells by changing deposition time and silane (SiH4) flow rate. The effects of carbon dioxide flow rate on the p-µc-SiO:H window and i-a-SiO:H buffer layer were also studied. Employing a p-µc-SiO:H/i-a-SiO:H/n-c-Si [Czochralski (CZ), 200 µm, (100)]/i-a-Si:H/n-a-Si:H configuration, we achieved an efficiency of 17.8% (active area efficiency) with an open-circuit voltage (Voc) of 665 mV. The solar cells showed a spectral response of about 0.83 at a wavelength of 400 nm, which is higher than that of conventional HJ solar cells with amorphous silicon window layers.

Fabrication of heterojunction solar cells by using microcrystalline hydrogenated silicon oxide film as an emitter

Wide gap, highly conducting n-type hydrogenated microcrystalline silicon oxide (?c-SiO?:?H) films were prepared by very high frequency plasma enhanced chemical vapour deposition at a very low substrate temperature (170??C) as an alternative to amorphous silicon (a-Si?:?H) for use as an emitter layer of heterojunction solar cells. The optoelectronic properties of n-?c-SiO?:?H films prepared for the emitter layer are dark conductivity = 0.51?S?cm?1 at 20?nm thin film, activation energy = 23?meV and E04 = 2.3?eV. Czochralski-grown 380??m thick p-type 1?0?0 oriented polished silicon wafers with a resistivity of 1?10???cm were used for the fabrication of heterojunction solar cells. Photovoltaic parameters of the device were found to be Voc = 620?mV, Jsc = 32.1?mA?cm?2, FF = 0.77, ? = 15.32% (active area efficiency).

Effect of Ambient Temperature on Performance of Grid-Connected Inverter Installed in Thailand

The effects of temperature on performance of a grid-connected inverter, and also on a photovoltaic (PV) system installed in Thailand have been investigated. It was found that the maximum efficiency of the inverter showed 2.5% drop when ambient temperature was above 37°C. The inverter performed efficiently in November and December, the months of high irradiance, and monthly average ambient temperature of lower than 35°C, allowing relatively high system performance ratio in this period. Our results show that high temperature provides negative impacts not only on the PV modules, but also on the performance of the inverter. Thus, the effect of temperature on the inverter efficiency should be taken into account when predicting energy yield or analyzing losses of the PV systems—especially in high temperature regions.

High efficiency a-Si:H/a-SiGe:H tandem solar cells fabricated with the combination of V- and U-shaped band gap profiling techniques

Hydrogenated amorphous silicon germanium (a-SiGe:H) films prepared by very high frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) using a mixture of SiH4, H2, and GeH4 were investigated for their use as the bottom cell of amorphous silicon/amorphous silicon germanium (a-Si:H/a-SiGe:H) tandem solar cell structures. Narrow optical band gaps (Eopt) in the range of 1.5 to 1.6 eV were obtained by varying the GeH4/(SiH4 + GeH4) gas flow rate ratio in low-temperature deposition. The a-SiGe:H films deposited with various GeH4/(SiH4 + GeH4) gas flow rate ratios were used as intrinsic layers for the a-Si:H/a-SiGe:H tandem solar cells with different graded band gaps: V-, VU-, and U-shapes. It was found that using the VU-shape improves the solar cell efficiency owing to a higher Jsc when compared with using V-shape. The VU-shape’s Voc and FF are also improved when compared with the U-shape’s Voc and FF. As a result, a high efficiency of 11.0% (Voc = 1.74 V, Jsc = 9.07 mA/cm2, and FF = 0.70) was successfully achieved with the solar cells fabricated using the VU-shape graded band gap technique.

Wide-Gap p-c-:H Films and Their Application to Amorphous Silicon Solar Cells

Optimization of p-type hydrogenated microcrystalline silicon oxide thin films (p-c-:H) by very high frequency plasma enhanced chemical vapor deposition 40 MHz method for use as a p-layer of a-Si:H solar cells was performed. The properties of p-c-:H films were characterized by conductivity, Raman scattering spectroscopy, and spectroscopic ellipsometry. The wide optical band gap p-c-:H films were optimized by CO2/SiH4 ratio and H2/SiH4 dilution. Besides, the effects of wide-gap p-c-:H layer on the performance of a-Si:H solar cells with various optical band gaps of p-layer were also investigated. Furthermore, improvements of open circuit voltage, short circuit current, and performance of the solar cells by using the effective wide-gap p-c-:H were observed in this study. These results indicate that wide-gap p-c-:H is promising to use as window layer in a-Si:H solar cells.

Effect of the CO2/SiH4 Ratio in the p-μc-SiO:H Emitter Layer on the Performance of Crystalline Silicon Heterojunction Solar Cells

This paper reports the preparation of wide gap p-type hydrogenated microcrystalline silicon oxide (p-c-SiO:H) films using a 40 MHz very high frequency plasma enhanced chemical vapor deposition technique. The reported work focused on the effects of the CO2/SiH4 ratio on the properties of p-c-SiO:H films and the effectiveness of the films as an emitter layer of crystalline silicon heterojunction (c-Si-HJ) solar cells. A p-c-SiO:H film with a wide optical band gap (E04), 2.1 eV, can be obtained by increasing the CO2/SiH4 ratio; however, the tradeoff between E04 and dark conductivity must be considered. The CO2/SiH4 ratio of the p-c-SiO:H emitter layer also significantly affects the performance of the solar cells. Compared to the cell using p-c-Si:H (CO2/SiH4 = 0), the cell with the p-c-SiO:H emitter layer performs more efficiently. We have achieved the highest efficiency of 18.3% with an open-circuit voltage () of 692 mV from the cell using the p-c-SiO:H layer. The enhancement in the and the efficiency of the solar cells verified the potential of the p-c-SiO:H films for use as the emitter layer in c-Si-HJ solar cells.

Advantages of N-Type Hydrogenated Microcrystalline Silicon Oxide Films for Micromorph Silicon Solar Cells

We report on the development and application of n-type hydrogenated microcrystalline silicon oxide films (n μc-SiO:H) in hydrogenated amorphous silicon oxide/hydrogenated microcrystalline silicon (a-SiO:H/μc-Si:H) micromorph solar cells. The n μc-SiO:H films with high optical bandgap and low refractive index could be obtained when a ratio of carbon dioxide (CO2) to silane (SiH4) flow rate was raised; however, a trade-off against electrical property was observed. We applied the n μc-SiO:H films in the top a-SiO:H cell and investigated the changes in cell performance with respect to the electrical and optical properties of the films. It was found that all photovoltaic parameters of the micromorph silicon solar cells using the n top μc-SiO:H layer enhanced with increasing the CO2/SiH4 ratio up to 0.23, where the highest initial cell efficiency of 10.7% was achieved. The enhancement of the open circuit voltage () was likely to be due to a reduction of reverse bias at subcell connection—n top/p bottom interface—and a better tunnel recombination junction contributed to the improvement in the fill factor (FF). Furthermore, the quantum efficiency (QE) results also have demonstrated intermediate-reflector function of the n μc-SiO:H films.