Microcrystalline Silicon P-layers Research Articles

Study of large area hydrogenated microcrystalline silicon p-layers for back surface field in crystalline silicon solar cells

A series of hydrogenated microcrystalline silicon (μc-Si:H) p-layers for back surface field in crystalline silicon solar cells were deposited on glass substrates by the developed large area (45 cm×45 cm) plasma enhanced chemical vapour deposition processor operating at 13.56 MHz and various values of source gas trimethylboron (TMB) to H2 flowratio. The influence of deposition parameters on the large area p-layer performance was intensively studied, as well as the thin film uniformity, optical, electrical and structural performances by Raman, FTIR, Ellipsometry, etc. Arrhenius and Tauc plots were used to discuss the μc-Si:H thin film’s activation energy and the defects state distribution. When amorphous-microcrystalline transition state was obtained, the deposited p-doped μc-Si:H layers showed specific resistance of 38.3 Ω−1cm−1 at the flowratio of 0.66% and high crystallinity of 45%–50% with no further treatment. The effect of source gas flowratio, deposition rate, and source gas partial pressure on μc-Si:H thin film’s performance was also investigated.

Surface morphology evolution of microcrystalline silicon p-layer prepared by RFPECVD

Surface morphology and crystallinity of silicon p-layer have been investigated on the effect of various deposition conditions of RFPECVD in order to clarify crystalline nuclei evolution. Crystallinity increased with increasing hydrogen dilution, but decreased with increasing both RF input power and diborane doping. Microcrystalline nuclei size increased with increasing working pressure, RF input power and substrate temperature. However, surface morphology was not correlated with crystallinity or deposition rate. A film with relatively large nuclei but having rather low crystallinity can be prepared for some condition, and vice versa. In order to get a dense microcrystalline silicon intrinsic layer subsequently deposited, surface morphology control of microcrystalline p-layer seems to be important as well as crystallinity.

High-Performance, Tandem-Type Amorphous Silicon Solar Cell

AbstractMicrocrystalline silicon oxide (μc-SiO) deposited from the gas mixture of silane and carbondioxide using VHF plasma was reported by authors to be the promising material for thin-film silicon solar cell fabricated on glass substrate, comparing with the conventional amorphous silicon oxide or microcrystalline silicon p-layer. High-performance, tandem-type solar cell with amorphous and microcrystalline cells (double cells) has been achieved by ap-plying this μc-SiO to the p-layer of both cells.Further work has been extended to a-Si tandem type solar cell with triple cell configu-ration using amorphous silicon oxide (a-SiO), amorphous silicon germanium (a-SiGe) and microcrystalline Si (μc-Si) as the top, middle and bottom cells, respectively. Up to now, cell efficiency of 15.7 % has been achieved using this novel μc-SiO.

Nanostructure in the p-layer and its impacts on amorphous silicon solar cells

The open circuit voltage (Voc) of n–i–p type hydrogenated amorphous silicon (a-Si:H) solar cells has been examined by means of experimental and numerical modeling. The i- and p-layer limitations on Voc are separated and the emphasis is to identify the impact of different kinds of p-layers. Hydrogenated protocrystalline, nanocrystalline and microcrystalline silicon p-layers were prepared and characterized using Raman spectroscopy, high resolution transmission electron microscopy (HRTEM), optical transmittance and activation energy of dark-conductivity. The n–i–p a-Si:H solar cells incorporated with these p-layers were comparatively investigated, which demonstrated a wide variation of Voc from 1.042V to 0.369V, under identical i- and n-layer conditions. It is found that the nanocrystalline silicon (nc-Si:H) p-layer with a certain nanocrystalline volume fraction leads to a higher Voc. The optimum p-layer material for n–i–p type a-Si:H solar cells is not found at the onset of the transition between the amorphous to mixed phases, nor is it associated with a microcrystalline material with a large grain size and a high volume fraction of crystalline phase.

Improved interface between front TCO and microcrystalline silicon p-i-n solar cells.

ABSTRACTThe microstructure of microcrystalline silicon p-layers on zinc oxyde (ZnO) has been studied by Transmission Electron Microscopy (TEM). ZnO has been characterised by X-Rays diffraction and by Scanning Electron Microscopy (SEM). These reveal that the ZnO surface topography consists of regular pyramids with a (110) preferential crystallographic growth axis. High Resolution TEM observations indicate that the p- layer growth starts at the top of the ZnO pyramids. This results, for fully microcrystalline p-layers, in a decreased thickness at the bottom of the ZnO pyramids. When the p-layer is fully microcrystalline, no amorphous incubation layer could be observed between ZnO and p-silicon layer. Moreover, the high crystallinity of the p-layers in microcrystalline p-i-n devices is accompanied by an increased fill-factor in the I-V characteristics.

Incorporation of p-type microcrystalline silicon films in amorphous silicon based solar cells in a superstrate structure

Thin (<20 nm) p-type microcrystalline silicon films have been deposited by plasma enhanced chemical vapor deposition in a parameter regime, specifically optimized for extremely thin films. High conductivity (>10 −2 Ω −1 cm −1) and low activation energy (<0.08 eV) have been achieved for thin films on various oxide substrates i.e., Corning 7059 glass, SnO 2 : F, TiO 2 and Ta 2O 5. Deposition of thin p-μc-Si : H is possible on void rich films (a-SiC : H and low-temperature deposited a-Si : H) but not on device quality a-Si : H. Single junction p-i-n cells were made in a superstrate structure using p-μc-Si : H as the window layer directly on top of SnO 2 : F coated glass. For the first time an efficiency of 9.63% could be achieved for a single junction cell with a truly microcrystalline silicon p-layer in a superstrate configuration. There is an improvement in the blue spectral response compared to the cell made with a-SiC : H(B) as window layer. However, open circuit voltage and fill factor were critically dependent on the choice of buffer layer at the p/i interface. Computer simulations point out that this can be attributed to the valence band offset between the amorphous i-layer and the microcrystalline p-layer. The buffer acts as a barrier to electron back-diffusion and reduces the recombination in the p-layer. Tandem cells (a-Si : H/a-Si : H) incorporating p-μc-Si : H along with n-μc-Si : H in the tunnel junction showed an efficiency of 9.9% and FF of 0.73. The tunnel junction n-μc-Si : H/p-μc-Si : H needed an oxide interface layer for a good performance. The role of the interface layer may be to increase the tunnel recombination as well as to act as a diffusion barrier to dopants.

Real time spectroscopic ellipsometry for characterization and optimization of amorphous silicon-based solar cell structures

Over the past few years, we have applied real time spectroscopic ellipsometry (RTSE) in order to characterize and optimize hydrogenated amorphous silicon (a-Si:H)-based solar cell fabrication by plasma-enhanced chemical vapor deposition (PECVD). Recently, the RTSE approach has been expanded to include the characterization of fine-grained microcrystalline silicon p-layers (μc-Si:H:B) deposited at low temperature (200°C) on a-Si:H i-layer substrates in the Cr/(n-i-p) solar cell configuration. In this study, we explore the effects of a H 2-plasma pre-treatment of the underlying i-layer on the resulting microstructural evolution and the optical properties of intended μc-Si:H:B p-layers, as deduced from a post-deposition analysis of the RTSE data. We find that film growth on an untreated underlying i-layer is in the form of a-Si:H:B even after 100 Å, whereas nanocrystallite nucleation occurs immediately under the same conditions on a H 2-plasma treated i-layer. Unique optical properties observed for the 50–150-Å thick μc-Si:H:B layers in device structures have been attributed to size effects in Si nanocrystals.

In-Situ Study of the Optoelectronic Properties of Very thin P-TYPE μc-Si:H Films and the Potential Profile at the p-(μc-Si:H)/i-(a-Si:H) Interface

ABSTRACTIn-situ UV-visible ellipsometry and Kelvin probe measurements were performed to study the growth of boron-doped microcrystalline silicon (μc-Si:H) thin films and the band profiling at the p- (μc-Si:H)/i-(a-Si:H) interface. The in-situ UV-visible spectroscopic ellipsometry measurements, combined with dark conductivity measurements, performed at different stages of the growth show that p-type μc-Si:H formation can be achieved for a film thickness below 10 nm. These analyses also reveal that both the optical absorption, and the dark conductivity do not change significantly for a crystalline volume fraction above 50%. Moreover, the contact potential as measured by in- situ Kelvin probe shows a saturation just after the percolation threshold. These results indicate that highly crystallized doped layers are not necessary in device applications. From the Kelvin probe measurements, the potential profile through the p-(μc-Si:H)/ i-(a-Si:H) interface was measured. The microcrystalline silicon p-layers were successfully incorporated in single junction solar cells.

Optoelectronic Properties of Thin Amorphous and Micro-Crystalline p-Type Films Developed for Amorphous Silicon-Based Solar Cells

AbstractVIIF-PECVD at 110 MI-z was used to deposit micro-crystalline p-layers on glass substrates for detailed analysis and onto ZnO coated substrates for incorporation into p-i-n solar cell structures. Solar cell and film analysis confirmed that the films incorporated into the solar cells contained significant crystalline silicon volume fractions despite being only 30 nm thick. The p-i-n solar cells employing a micro-crystalline silicon p-layer deposited on ZnO coated substrates had series resistances, fill factors and Voc similar to those of the reference solar cells deposited onto SnO2 coated substrates and having optimized amorphous silicon-carbon p-layers. The short circuit current of the micro-crystalline p-layer case was 10 percent lower than that of the reference cell indicating that further optimization is required.