Search

Silicon nanocrystal quantum dots in a dielectric matrix form a material with higher band gap than silicon, but still compatible with silicon technology. So far, devices using silicon nanocrystals have been realized either on silicon wafers, or using in-situ doping in the superlattice deposition which may hinder the nanocrystal formation. In this paper, a vertical PIN device is presented which allows to investigated the electrical and photovoltaic properties of nanocrystal quantum dot layers. The device structure circumvents any influence of a substrate wafer or dopants and provides full flexibility in the material choice of both, i.e. electron and hole, contacts. Furthermore, not-high-temperature stable contact materials can be applied. Devices have been realized using SiC/Si nanocrystal multilayers as the i-region and doped a-SixC1-x:H layers as electron and hole contacts. First devices show open-circuit voltage of up to 400mV.

In this paper the applicability and efficiency of different intermediate layer (IL) stacks for the implementation in recrystallized wafer equivalent (RexWE) solar cells are investigated. The requirements for the IL in the RexWE concept are short term stability at temperatures above 1400 °C, high reflectivity for wavelengths exceeding 600 nm, electrical conductivity and acting as a diffusion barrier against metallic impurities. Various combinations of stoichiometric SiC layers, silicon rich SiC layers and SiO 2 layers were tested as IL stacks regarding their performance after a zone melting recrystallization (ZMR) process. For the first time, samples with an IL consisting of a SiC multilayer were recrystallized and successfully processed to solar cells.

The subject of this work is the development of an electrically conductive Rugate filter for photovoltaic applications. We believe that the optical as well as the electrical performance of the filter can be adapted especially to the requirements of crystalline Si thin-film and amorphous/crystalline silicon tandem solar cells. We have deposited amorphous hydrogenated silicon carbide layers (a-Si x C 1-x :H) with the precursor gases methane (CH 4 ), silane (SiH 4 ) and diborane (B 2 H 6 ) by applying Plasma Enhanced Chemical Vapour Deposition (PECVD). By variation of the precursor flows, a floating refractive index n from 1.9 to 3.5 (at 633 nm) could be adjusted quite accurately. Different complex layer stacks (up to 200 layers) with a sinusoidal refractive index variation normal to the incident light were deposited in just 80 min on an 100x100 mm 2 area. Transmission measurements show good agreement between simulation and experiment, which proves our ability to control the deposition process, the good knowledge of the optical behaviour of the different SiC single layers and the advanced stage of our simulation model. The doped single layers show lateral conductivities that were extremely dependent on the Si/C ratio.

An effective light trapping system is required in silicon solar cells in order to collect a large amount of photons. That is why we focus our investigation on the fabrication and evaluation of two types of optical systems introduced on the back side of solar cells. The aim of these structures is to enhance the light trapping of the long wavelength photons (above 1000 nm). On the one hand, we evaluated a Si/SiO2 linear nanograting; on the other hand, hexagonal nanostructures fabricated with SiO2 nanoparticles and a filling matrix are under investigation. In this paper, we describe the fabrication processes developed for both approaches and we present the solar cell results and characterisation. For the first approach, we show a reflectance reduction on test structures, which occurs at the same wavelength as the increase of absorption induced by the simulated gratings. Moreover, we demonstrate the feasibility of the fabrication of silicon solar cells with the hexagonal nanostructures as a diffractive back reflector. Although no short circuit current increase has been observed due to a poor rear side passivation, a current gain up to 0.3 mA/cm2 is possible in the wavelength range of 1050-1150 nm due to these nanostructures. Finally, we also comment on the advantages and drawbacks of each approach and on the feasibility to introduce these systems in the solar cell process flow.