When applying a silver nanoparticles layer on p-i-n structure that will lead to increase the current generated in thin-film solar cells due to the light trapping effect 36-38.
1.3.4. Advantages of second generation solar cell
1. Economically properties, due to using cheap substrates and low quantity of deposited raw materials 39
2. The modules are light and have handling easily feature.
4. They are flexible compared with c-Si cells which are brittle.
5. The ability to be inserted into building roofs and facades.
6. Thin film solar cell can be produced with large sizes with high production rate. So it can meet market needs 39, 40.
1.3.5. Disadvantages of second generation solar cells
1. They are lower efficiency than c-Si solar cells 41.
2. Instability feature, amorphous silicon thin film solar cells degrade with time 42.
3. Optical losses.
4. Using toxic material during the production 43.
1.4. Deposition techniques of thin film solar cells
Many deposition techniques can be used to produce the solar cell thin film. These techniques generally divided into two basic techniques, chemical vapor deposition CVD and physical vapor deposition PVD with their different types that illustrated in detail in the following sections.
The main different between CVD and PVD techniques is that the input row material at CVD process is in a gas form that a chemical reaction between the gases occur at the device chamber near a substrate surface. whereas, in PVD involve transfer a material on an atomic level , this material start out in solid form and vaporized during deposition process. Figures 1.6 and 1.7 showing how CVD and PVD process occur. CVD and PVD techniques have several process types, these processes can be used according to applications and required functions of the coated component 44, 45.
This thesis including two sector, first we used PECVD process to produce p-i-n thin film solar cell on a TCO glass substrate, then build on the produced thin film solar cell a layer of silver nanoparticles on n layer using PVD to enhancement the light trapping. So it is worthwhile to briefly compare CVD technique with PVD technique in order to realize the significance of both techniques and technological niche marketing 46. The comparison between the two techniques is shown in Table 1.2.
1.4.1. Chemical vapor deposition CVD
Several process types of CVD can be used for produce Si thin film solar cell Process types of CVD techniques is shown in Figure 1.8 47, each type has its own merits and drawbacks. Among these techniques, Plasma Enhanced Chemical Vapor Deposition (PECVD) is the only technique that provides a homogeneous and excellent film with low temperature that the glass substrate can stand on.
Plasma Enhanced Chemical Vapor Deposition is an ideal process to fabricate thin film solar cells. Several parameters need to be controlled in this process. PECVD is based on the dissociation of a silicon source gas in a plasma and subsequent deposition on a heated substrate.
1.4.2. Physical vapor deposition PVD
Physical vapor deposition is a vaporization coat¬ing technique, the material transfers on an atomic level. The difference between the chemical vapor deposition (CVD) and the physical vapor deposition (PVD). It has a wide range of application due to that in this technique different substrate materials can be deposited such as polymers, ceramic, alloys, glass and metals. On the other hand different coated material can be used as semiconductors, metals, metal oxides, alloys and cermets. PVD advantages included that the deposition can be performed at low substrate temperature and complex structure can be deposited with good adhesion. Physical Vapor Deposition PVD technique including also several process types are shown in Figure 1.9 49.
1.5. Outline of Thesis
In this work we investigate the combined effect of the gas dilution ratio rH and the substrate temperature TS manufacturing parameters for the i-layer on the transition from amorphous to microcrystalline structure. PECVD technique is used to deposit i-layer ITO glass substrate with different gas dilution ratios rH and different substrate temperatures TS. The i-layer will be evaluated by atomic force microscopy (AFM), X-ray Diffraction (XRD) and field emission scanning electron microscopy (FESEM). After the transition region is detected we used its specific deposition condition to build p-i-n junction by PECVD. This was followed by depositing a thin layer of silver nanoparticles on this p-i-n junction using PVD technique at different substrate temperatures to correlate the morphology characteristics with the conversion efficiency and the optical properties of a-Si:H/?c-Si:H thin-film solar cell. The effect of substrate temperature of silver nanoparticles thin layer by the PVD process on the efficiency and the optical absorption will be studied current -voltage and optical absorption measurements.