Volker Steenhoff

Comparison of Ag and SiO2 Nanoparticles for Light Trapping Applications in Silicon Thin Film Solar Cells.

Plasmonic and photonic light trapping structures can significantly improve the efficiency of solar cells. This work presents an experimental and computational comparison of identically shaped metallic (Ag) and nonmetallic (SiO2) nanoparticles integrated to the back contact of amorphous silicon solar cells. Our results show comparable performance for both samples, suggesting that minor influence arises from the nanoparticle material. Particularly, no additional beneficial effect of the plasmonic features due to metallic nanoparticles could be observed.

Laser perforated ultrathin metal films for transparent electrode applications

Transmittance and conductivity are the key requirements for transparent electrodes. Many optoelectronic applications require additional features such as mechanical flexibility and cost-efficient fabrication at low temperatures. Here we demonstrate a simple method to fabricate high performance transparent electrodes that is based on perforation of thin silver layers using picosecond laser pulses. Transparent electrodes have been characterized optically and electrically in order to determine the influence of specific surface coverage. Special attention was paid to maintaining sufficient conductivity in the metal-free areas. As a result, transmittance of a much higher bandwidth was achieved as compared to unpatterned metal films. Transparent electrodes have been fabricated on glass and plastic foil, as well as wafer-based silicon heterojunction solar cells, demonstrating their applicability for most relevant cases.

Optimized Optical Field Profile in Resonant-Cavity-Enhanced a-Ge:H Nanoabsorber Solar Cells for Tandem Cell Application

Amorphous germanium-based solar cells exploiting second-order Fabry-Pérot resonances can reach strong infrared absorption with an absorber thickness of either 25 nm or less. Hence, they are a promising candidate for the replacement of micrometer-thick μc-Si:H bottom cells in a-Si:H/μc-Si:H tandem configurations. Here, we present a detailed experimental and simulation-aided analysis of the optical properties of such devices, with a particular focus on their potential application in the tandem cells. A clear relation of the results to the field profile inside the cavity was found, and guiding rules for optimization are deduced. By modeling the transmission behavior of an a-Si:H top cell, we evaluate the potential of the fabricated devices for tandem cell application, allowing a benchmark against μc-Si:H solar cells. The best sample was found to enable a tandem cell performance equivalent to a μc-Si:H bottom device reaching 5% single cell efficiency.