We developed a procedure for the electrodeposition of fluorescent silicon nanomaterial from silicates on conducting substrates. The electrodeposion solution used is a solution of sodium metasilicon salts (Na2SiO3) in HF/H2O2. When a positively biased platinum substrate is immersed in the bath, a current is drawn and a thin fluorescent coating is formed on the substrate. We discuss the results in terms of current-induced nucleation of silicon nanostructures.

Device-quality hydrogenated amorphous silicon (a-Si:H) thin films grown under conditions where the SiH3 radical is the dominant deposition precursor are remarkably smooth, as the SiH3 radical is very mobile and fills surface valleys during its diffusion on the a-Si:H surface. In this paper, we analyze atomic-scale mechanisms of SiH3 diffusion on a-Si:H surfaces based on molecular-dynamics simulations of SiH3 radical impingement on surfaces of a-Si:H films. The computed average activation barrier for radical diffusion on a-Si:H is 0.16 eV. This low barrier is due to the weak adsorption of the radical onto the a-Si:H surface and its migration predominantly through overcoordination defects; this is consistent with our density functional theory calculations on crystalline Si surfaces. The diffusing SiH3 radical incorporates preferentially into valleys on the a-Si:H surface when it transfers an H atom and forms a Si-Si backbond, even in the absence of dangling bonds.

Poly-crystalline Si and Ge layers were grown at low temperatures on glass substrates by successive hydrogenation and annealing steps, with no need to any metal incorporation. Hydrogenation is performed in an RF-PECVD apparatus with different powers of hydrogen plasma and the annealing step is carried out in the same system in N2 ambient. This leads to formation of granular Si and Ge structures with average grain size of less than 100nm at temperatures as low as 250°C and 150°C, respectively. The effect of hydrogen plasma power at various temperatures on the crystallinity of the layers has been studied by SEM and TEM analyzes. Successive hydrogenation and annealing at respective temperatures of 150°C and 200°C for Ge layer and 300°C for Si layer would result in a device-quality polycrystalline Ge and Si layers which have been employed for fabrication of thin-film transistors. These TFTs show the mobility of 80cm2/Vs and 4cm2/Vs and ON/OFF ratio of more than 103 and 5×104 for Ge and Si, indicating the feasibility of this technique for applications in large-area electronics.

For SiCl4-based microcrystalline silicon films the doping dependence of chlorine and hydrogen incorporation was studied. The results reveal a Fermi level dependence with a maximum chlorine (and hydrogen) incorporation for a Fermi level somewhat above midgap. As an explanation, a Fermi level dependence of the chlorine release rate during film growth is considered, similar as valid for hydrogen diffusion and desorption.

A novel light trapping scheme is developed to enhance the optical path length in solar cells by using a photonic structure as the backside reflector. This structure combines a reflection grating on the substrate with an over-deposited distributed Bragg reflector (DBR). With this structure, the optical path length can be enhanced by more than 104 times with very little reflection loss. In turn, solar cell efficiency is predicted to be enhanced enormously.

Silicon heterojunction cells (SHJ) using crystalline silicon wafers and deposited heterojunction thin film emitters are interesting from an economical, technological, and sc ientific point of view. Modules using such cells (so called HIT cells) are commercially produced by Sanyo Electric Co., using single crystal wafers. Recently reported alternatives still comprise a high-temperature diffused back surface field (BSF). In order to provide a low cost alternative, our goal is to develop SHJ using multicrystalline silicon wafers with both a deposited emitter and a deposited BSF. The present approach truly allows the development of a cheap, low temperature, all-deposited alternative for the HIT cell.

We made a bifacial silicon heterojunction solar cell, with an emitter consisting of a 7 nm intrinsic a-Si:H layer and a 15 nm n-type μc-Si:H layer. The back surface field is formed by a 30 nm p++ μc-Si:H layer. In order to achieve a functional deposited BSF the thin p++-layer has to have higher effective dopant concentration than the substrate. We used a 375 μm thick FZ wafer with a resistance of 1 cm with an activation energy of 0.2 eV. The μc-Si:H p++-layer has an activation energy of Ea = 0.082 eV. To detect the operation of the BSF the cell was made bifacial. The cell has an efficiency of 14.87 %, Voc = 571.4 mV and Jsc = 33.3 mA/cm2, Rs = 1.2 Ωcm2 and Rp = 1.8 kΩcm2. The cell, illuminated from the back, shows a Voc of 0.1 V and Jsc of 7 mA/cm2. Reference bifacial cells without BSF show no cell behavior illuminated from the rear side. External quantum efficiency (EQE) measurements with illumination at the rear side of the bifacial heterojunction cell with BSF show a quantum efficiency value of 0.17 in the range 500-800 nm, while the reference cell without BSF shows zero quantum efficiency in this range. These results show evidence for the feasibility of a truly functioning deposited BSF combined with a SHJ with deposited emitter.

We have developed highly stabilized (p-i-n)-type protocrystalline silicon (pc-Si:H) multilayer solar cells. However, the source of the superior light-induced stability of the pc-Si:H multilayer absorbers compared to conventional amorphous silicon (a-Si:H) absorbers remains unclear. Photoluminescence (PL) and Fourier transform infrared (FTIR) spectroscopy measured at room temperature produce strong evidence that nano-sized silicon grains embedded in regularly arranged highly H2-diluted sublayers suppress the photocreation of dangling bonds. To achieve a high conversion efficiency, we applied a double-layer p-type amorphous siliconcarbon alloy (p-a-Si1-xCx:H) structure to the pc-Si:H multilayer solar cells. The less pronounced initial short wavelength quantum efficiency variation as a function of bias voltage, and the wide overlap of dark current - voltage (JD-V) and short-circuit current - open-circuit voltage (Jsc-Voc) characteristics prove that the double p-a-Si1-xCx:H layer structure successfully reduces recombination at the p/i interface. Thus, we achieved a highly stabilized efficiency of 9.0 % without any back reflector.