Performance Of μc-Si Research Articles

Development of n-type microcrystalline SiOx:H films and its application by innovative way to improve the performance of single junction µc-Si:H solar cell

Light trapping is one of the fundamental necessities of thin film based solar cell for its performance elevation. Back reflection of unused light of first pass is the key way to improve the light trapping phenomena. In this study we have reported the development of n-type hydrogenated microcrystalline silicon oxide (n-µc-SiO:H) layers of different characteristics. The deposition has been done by Plasma Enhanced Chemical Vapor Deposition (PECVD) technique. The detailed characterization of the films include the following: (1) electrical properties (2) optical properties like E04 (3) structural studies which include crystalline fraction by Raman spectroscopy and grain size by X-ray diffraction measurement, FTIR spectroscopy, AFM and TEM studies. n-µc-SiO:H layer has been introduced as the n-layer of single junction p–i–n structure µc-Si solar cells. By various techniques the optimum use of n-µc-SiO:H layer for enhancing the performance of µc-Si:H solar cells has been done. It has been found that by using suitable bilayer of two different n-µc-SiO:H layers, it is possible to increase the solar cell performances. The maximum efficiency obtained without any back reflector is 8.44% that is about 8.9% higher than that obtained by using n-µc-Si:H layer as n-layer in the solar cells.

Relationship between absorber layer defect density and performance of a‐Si:H and µc‐Si:H solar cells studied over a wide range of defect densities generated by 2 MeV electron bombardment

We summarize an extensive study on the impact of absorber layer defect density on the performance of amorphous (a-Si:H) and microcrystalline (μc-Si:H) silicon solar cells. To study the effects of the absorber layer defect density we subjected set of a-Si:H and μc-Si:H cells to a 2MeV electron bombardment. Subsequently the cells were stepwise annealed to vary the defect density. The cells have varying thicknesses and are illuminated from either the p- or n-side. For reference we subjected i-layers to the same treatment as the cells. The procedure enabled the reversible increase of the i-layer defect density (NS) with two orders of magnitude according to electron spin resonance measurements (ESR) performed on reference samples. The large variation of NS induces substantial changes in the current–voltage characteristics (J–V) and the external quantum efficiency spectra (EQE). These changes in device characteristics provide a solid reference for analysis and device simulations. It was found that performance of a-Si:H cells degraded weakly upon NS increase up to 1017cm−3 and dropped steeply as defect density was increased further. In contrast, performance of µc-Si:H cells showed continuous reduction as NS raised. By comparing p- and n-side illuminated cells we found that, for NS above 1017cm−3, the p-side illuminated a-Si:H cells outperformed the n-side illuminated ones, however, the difference was barely visible at NS below 1017cm−3. On the contrary, the device performance of n-side illuminated µc-Si:H cells was much more affected by the increase in defect density, as compared to the p-side illuminated cells. EQE results evidenced a significant asymmetry in collection of electrons and holes in µc-Si:H devices, where carrier collection was limited by holes as defect density was increased. Based on the experimental data we speculate that the improvement of absorber material in terms of as-deposited defect density is not of primary importance for the performance of a-Si:H cells, whereas in μc-Si:H based solar cells, the reduction of the absorber layer defect density below the state-of-the-art levels, seems to improve the cell performance.

Optimization of n/i and i/p buffer layers in n–i–p hydrogenated microcrystalline silicon 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 was studied in detail. The experimental results demonstrated that the efficiency is much improved when there is a higher crystallinity at n/i interface and an optimized a-Si:H buffer layer at i/p interface. By combining the above methods, the performance of μc-Si:H single-junction and a-Si:H/μc-Si:H tandem solar cells has been significantly improved.

Effects of p-seeding layer on the performance of microcrystalline silicon solar cells deposited in single chamber

The p-i-n type μc-Si:H solar cells were prepared in a single chamber using very high frequency plasma enhanced chemical vapor deposition technique. Boron cross-contamination between p-layer and subsequent i-layer seriously affects the device performance. The effects of p-seeding on the μc-Si:H i-layers and performance of μc-Si:H solar cells were investigated.The p-seeding method was mainly realized by relatively high hydrogen rich plasma. It has been demonstrated that p-seeding can improve the characteristics of p/i interface and the vertical uniformity of the intrinsic layer and reduce boron contamination. Through the optimization of p-seeding layer technique, a-Si:H/μc-Si:H tandem solar cell with 881% （1 cm2） conversion efficiency has been fabricated in single chamber.

High efficiency microcrystalline silicon solar cells with Hot-Wire CVD buffer layer

Microcrystalline silicon (μc-Si:H) solar cells with i-layers deposited by hot wire chemical vapor deposition (HWCVD) exhibit higher open circuit voltage and fill factor than the cells with i-layers deposited by plasma enhanced (PE)-CVD. Inserting an intrinsic μc-Si:H p/ i buffer layer prepared by HWCVD into PECVD cells nearly eliminates these differences. The influence of buffer layer properties on the performance of μc-Si:H solar cells was investigated. Using such buffer layers allows to apply high deposition rate processes for the μc-Si:H i-layer material yielding a high efficiency of 10.3% for a single junction μc-Si:H solar cell.

Effects of seeding methods on the fabrication of microcrystalline silicon solar cells using radio frequency plasma enhanced chemical vapor deposition

Single junction p-i-n μc-Si:H solar cells were prepared in a low-cost, large-area single chamber radio frequency plasma enhanced chemical vapor deposition system. The effects of seeding processes on the growth of μc-Si:H i-layers and performance of μc-Si:H solar cells were investigated. Seeding processes, usually featured by highly hydrogen rich plasma, are effective in inducing the growth of μc-Si:H i-layers. It has been demonstrated that p-layer seeding methods are preferable to i-layer seeding. While performance of μc-Si:H solar cells produced by i-layer seeding methods was usually limited by very low fill factors, μc-Si:H solar cells with good initial and stabilized conversion efficiencies were obtained by p-layer seeding.

Microcrystalline silicon films and solar cells deposited by PECVD and HWCVD

The application of microcrystalline silicon (μc-Si:H) in thin-film solar cells is addressed in the present paper. Results of different technologies for the preparation of μc-Si:H are presented, including plasma enhanced chemical vapour deposition (PECVD) using 13.56 MHz (radio frequency, rf) and 94.7 MHz (very high frequency, vhf) and hot-wire chemical vapour deposition (HWCVD). The influence of the silane concentration (SC) on the material and solar cell parameters is studied for the different techniques as the variation of SC allows to optimise the solar cell performance in each deposition regime. The best performance of μc-Si:H solar cells is always observed near the transition to amorphous growth. The highest efficiency obtained so far at a deposition rate of 5 Å/s is 9.4%, achieved with rf-PECVD in a deposition regime of using high pressure and high discharge power. High deposition rates and solar cell efficiencies could be also achieved by vhf-PECVD. An alternative approach represents the HWCVD which also demonstrated high deposition rates for μc-Si:H. However, good material quality and solar cell performance could only be achieved at low substrate temperatures and, consequently, low deposition rates. The μc-Si:H solar cells prepared by HWCVD exhibit comparably high efficiencies up to 9.4% and exceptionally high open circuit voltages up to 600 mV but at lower deposition rates (≈1 Å/s). The properties of PECVD and HWCVD solar cells are carefully compared.