The Researches On Thin Film Photovoltaic Technology Based On Si Nanostructures

As solar energy is inexhaustible, clean and renewable, the efficient utilization of solar energy can resolve the energy crisis effectively. However, the classical fossil fuel cannot be replaced by the solar energy until now, which is caused by the high cost and low efficiency of solar cells. In order to enhance the photoelectric conversion ability of solar cells and reduce the cost of their fabricating process, this thesis has devoted to several works on investigating the performances of the nanostructures based thin film solar cells.The parameters of the thin film Si nanowires arrays and Si nanocones arrays solar cells have been optimized. The performances of the SiNWs and SiNCs arrays thin film solar cell with different structural parameters have been investigated. The structural parameters of the thin film solar cell, such as the filling ratio, the period and the length of the SiNWs and SiNCs can affect the ultimate conversion efficiency greatly. For 3?m SiNW arrays thin film solar cells, with or without the silicon substrates, the obtained corresponding optimizing ultimate efficiency reach to 24.07% and 21.99% respectively, and that of the SiNC arrays solar cells can reach to 31.39% nearly. This thesis has also discussed the simulated results based on the multiple reflection effects, the graded refractive index theory, and guiding modes coupling effectA novel silicon solar cell with the tapered nanoholes arrays (TNHs) have been proposed for the efficient light trapping. After the optimization of the structural parameters, a value of ultimate conversion efficiency (UCE) about 28.6% for the TNHs solar cells with the thickness of active layer of only 1?m have been obtained. And the performance of the TNHs solar cells is better than those of the existing cone-shaped nanoholes arrays (CNNHs) and the pure nanoholes arrays (NHs). The Ag nanoparicles (AgNPs) can be formed automatically during the process of manufacturing the Ag backreflector (AgBR) for the TNHs solar cells. The influences of the structural parameters of AgNPs on the performance of the solar cell have also been investigated systematically, and the corresponding optimal UCE can reach to 30.1% nearlyA novel thin film solar cell with dual photonic crystals has been proposed, which shows an advanced light trapping effect and superior performance in ultimate conversion efficiency (UCE). The shapes of the nanocones at the front and back side of active layer have been optimized and discussed in detail by self-definition. The optimized shape of nanocones arrays (NCs) is the parabolic-shape with nearly linearly graded refractive index (GRI) profile from the air to Si, and the corresponding UCE is 30.3% for the NCs with the period of 300nm and the thickness of only 2?m. The top NCs and bottom NCs of the thin film have been simulated respectively to investigate their optimized shapes, and their separate contributions to the light harvest have also been discussed fully. The height of the top NCs and bottom NCs will also influence the performances of the thin film solar cell greatly, and the result indicates that the unconformal NCs have better light trapping ability with the optimal UCE reaching to 32.3% than the conformal NCs with the optimal UCE reaching to 30.3%.The optical properties of the various types of tapered silicon nanowires arrays (SiNWs) have been investigated by the phase retrieving method based on the experimental reflection spectra and the Kramers-Kronig (KK) relation. The effective refractive index (n) and the extinction coefficient (K) of each tapered SiNWs and combined silicon nanowires and microwires (CNMW) array samples can be obtained from concrete simulation by the KK relation. At the same time, the real part (?') and imaginary part (?") of the effective complex dielectric constant can also be obtained from the relation between the refractive index and the complex dielectric constant of samples. And the simulated results show that the relative material parameters (effective complex refractive index, effective complex dielectric function) can be modulated from a concrete material processing.