Junming Xue

HIGH GROWTH-RATE DEPOSITION OF μc-Si:H THIN FILM AT LOW TEMPERATURE WITH VHF-PECVD

High growth rate deposition of μc-Si:H film with VHF-PECVD at low temperature has been reported. Investigations showed that growth rates enhanced with higher excitation frequency and working pressure, but increased at first then decreased with the increase of plasma power. Optical emission spectroscopy (OES) was introduced to monitor VHF plasma. The relationship between the growth rates and the OES results has been discussed. Raman spectra were also used to study the a-Si:H/μc-Si:H phase transition. Finally a high growth rate of 2.0nm/s has been obtained through the initially optimized condition.

Effect of pretreatment on PET films and its application for flexible amorphous silicon solar cells

We proposed a low cost solution of flexible amorphous silicon solar cells on Polyethylene terephthalate(PET) polymer substrates deposited at low temperatures. PET films were firstly annealed both in the air and in vacuum at different temperatures, and the properties of PET films after annealing were evaluated. Then PET films were exposed to glow discharge Argon plasma in a standard PECVD system to improve their surface properties. The relationship between glow discharge parameters and the energy of Ar plasma were investigated by OES. After Ar plasma treatment, not only the surface morphology of PET but also the adhesion of the solar cell thin films to the PET substrates were improved. Finally, single junction a-Si solar cells with a p-i-n superstrate type were fabricated on PET/ITO substrates at low temperature of Ts=125°C, and an initial efficiency of 4.8% was obtained.

Hydrogenated Microcrystalline Silicon Single-Junction Nip Solar Cells

The microstructural properties of hydrogenated microcrystalline silicon solar cells are investigated using Raman spectroscopy and x-ray diffraction. It was found that the increase of grain size and crystalline volume fraction with thickness is the main reason for the deterioration of cell performance as using constant hydrogen dilution technique. In order to adjust grain size and crystalline volume fraction along the growth direction, gradient hydrogen dilution technique has been adopted to control the structural evolution. The experiment results demonstrated that the performance of solar cell can be much improved when there’s a higher crystallinity at n/i interface and a lower crystallinity at i/p interface. We have achieved an initial active-area efficiency of 5.7% (Voc=0.47V, Jsc=20.2mA/cm2, FF=60%) for the µc-Si:H single-junction n-i-p solar cells.

The research of N/I and I/P buffer layers in μC-Si:H N-I-P single-junction solar cells

Hydrogenated microcrystalline silicon (μc-Si:H) intrinsic films and solar cells with n-i-p configuration were prepared by plasma enhanced chemical vapor deposition (PECVD). The influence of n/i and i/p buffer layers on the μc-Si:H cell performance were studied in detail. The experimental results demonstrated that the efficiency can be much improved when theres a higher crystallinity at n/i interface and an optimized a-Si:H buffer layer at i/p interface. By combining above methods, the performance of μc-Si:H single-junction and a-Si:H/μc-Si:H tandem solar cells has been significantly improved.

Study of P-µC-Si1-XGex:H Thin Film by Vhf-Pecvd

In this paper, a series of boron doped microcrystalline hydrogenated silicon-germanium (P-µc-Si1-xGex:H) was deposited by very high frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) at different GeF4 concentration (GC=[GeF4]/[GeF4]+[SiH4]). The Ge fraction x was measured by XRF and the conductivity was measured by the coplanar conductivity measurement. The results showed that, with the increasing of GC, the Ge fraction x increases slowly first, then increases linearly and the dark conductivity increases first, then decreases. The results of Raman measurement evidently showed that the crystalline volume fraction of p-type microcrystalline silicon germanium increased small and then decreased as the GC increased. When the GC is 4%, p-µc-Si1-xGex:H material with high conductivity, low activation energy (σ = 1.68S/cm, Eg = 0.047ev) and high crystalline volume fraction at the thickness of 72nm was achieved. The experimental results were discussed in detail.

Microcrystalline Silicon Materials and Solar Cells with High Deposition Rate

Although similar deposition rate (2.0nm/s) and defect absorption (α0.8eV =2.5cm-1) for intrinsic µc-Si:H films can be obtained at different total gas flow rate, the solar cell performance, which consists of the above intrinsic µc-Si:H as absorb layers, was obviously different. From the results of quantum efficiency (QE), dark J-V characteristic and Raman spectra, it was found that the amorphous silicon incubation layer is the main reason for the difference of the two solar cells. Increased the total gas flow rate can reduce the thickness of the amorphous silicon incubation layer, which can enhanced the QE response in the long wavelength and increase the short circuit current. These results demonstrate that the amorphous silicon incubation layer was a key factor for the fabrication of high efficiency microcrystalline silicon solar cell with high growth rate.

Development of single and micromorph tandem solar cells in n-i-p configuration with high-pressure RF-PECVD deposited doped and active layers

This paper gives an overview of the scientific challenges and achievements during the development of thin film silicon based single and tandem solar cells with high-pressure RF-PECVD deposited doped and active layers. The effect of i/p interface treatment on the crystalline growth of high conductive p-type layer and the improvement of the Voc and FF of single-junction a-Si:H solar cell was studied. The role of gradient hydrogen dilution technique in the controlling the microstructural evolution of the intrinsic layer and its influence on the solar cell performance were investigated. By combining above methods, an efficiency of 5.7% (Voc=470mV, Jsc=20.2mA/cm2, FF=60%) has been for a single-junction μc-Si:H solar cell. Then, the thicknesses of bottom cells and top cells were varied to achieve good current matching, which yield an efficiency of 9.9% for μc-Si:H/a-Si:H tandem solar cell with Voc of 1221mV, Jsc of 11.61mA/cm2 and fill factor of 70%.

High Rate Deposition of Stable Hydrogenated Amorphous Silicon in Transition from Amorphous to Microcrystalline Silicon

High rate deposition of high quality and stable hydrogenated amorphous silicon (a-Si:H) films were performed near the threshold of amorphous to microcrystalline phase transition using a very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) method. The effect of hydrogen dilution on optic-electronic and structural properties of these films was investigated by Fourier-transform infrared (FTIR) spectroscopy, Raman scattering and constant photocurrent method (CPM). Experiment showed that although the phase transition was much influenced by hydrogen dilution, it also strongly depended on substrate temperature, working pressure and plasma power. With optimized condition high quality and high stable a-Si:H films, which exhibit σ ph /σ d of 4.4×10 6 and deposition rate of 28.8A/s, have been obtained.