Showing papers by "Nicolas Wyrsch published in 2017"

Review: Progress in solar cells from hydrogenated amorphous silicon

Abstract: Hydrogenated amorphous silicon (a-Si:H) has been used for decades—doped and as intrinsic absorber layers—in thin-film silicon solar cells. Whereas their effiency was improved for a long time by the deposition of higher quality absorber layers, recent improvements can be attributed to a better understanding of the interfaces, allowing for their specific engineering. In this review, we briefly resume the state-of-the-art of a-Si:H solar cell technology from growth and characterization of single layers to full solar cells and multijunction devices. Focusing on the absorber layer quality first, we highlight thereafter aspects of interface problematics and discuss the growth and role of doped microcrystalline silicon-oxide layers and approaches of 3D-solar-cell designs in more detail. Although the findings summarized in this review were obtained from thin-film solar cells, we show that a-Si:H is a very versatile material with properties that are of high interest for application in other devices such as heterojunction solar cells, detectors, or optoelectronic devices.

The impact of silicon solar cell architecture and cell interconnection on energy yield in hot & sunny climates

Abstract: Extensive knowledge of the dependence of solar cell and module performance on temperature and irradiance is essential for their optimal application in the field. Here we study such dependencies in the most common high-efficiency silicon solar cell architectures, including so-called Aluminum back-surface-field (BSF), passivated emitter and rear cell (PERC), passivated emitter rear totally diffused (PERT), and silicon heterojunction (SHJ) solar cells. We compare measured temperature coefficients (TC) of the different electrical parameters with values collected from commercial module data sheets. While similar TC values of the open-circuit voltage and the short circuit current density are obtained for cells and modules of a given technology, we systematically find that the TC under maximum power-point (MPP) conditions is lower in the modules. We attribute this discrepancy to additional series resistance in the modules from solar cell interconnections. This detrimental effect can be reduced by using a cell design that exhibits a high characteristic load resistance (defined by its voltage-over-current ratio at MPP), such as the SHJ architecture. We calculate the energy yield for moderate and hot climate conditions for each cell architecture, taking into account ohmic cell-to-module losses caused by cell interconnections. Our calculations allow us to conclude that maximizing energy production in hot and sunny environments requires not only a high open-circuit voltage, but also a minimal series-to-load-resistance ratio.

Amorphous silicon-based micro-channel plate detectors with high multiplication gain

Abstract: With their fast response time and a spatial resolution in the range of a few microns, microchannel plates (MCPs) are a prominent choice for the development of detectors with highest resolution standards. Amorphous silicon-based microchannel plates (AMCPs) aim at overcoming the fabrication drawbacks of conventional MCPs and the long dead time of their individual channels. AMCPs are fabricated via plasma deposition and dry reactive ion etching. Using a state-of-the-art dry reactive ion etching process, the aspect ratio, so far limited to a value of 14, could be considerably enhanced with a potential for very high gain values. We show first fabricated AMCP devices and provide an outlook for gain values to be expected based on the fabrication results.

Notice of Removal Microcrystalline silicon carrier collectors for silicon heterojunction solar cells and impact on low-temperature device characteristics

Abstract: Silicon heterojunction solar cells usually employ doped amorphous silicon layers as carrier selective contacts. However, these layers may cause parasitic optical absorption losses and moderate fill factor values due to high contact resistivity with the transparent electrodes. In this study, we show that the replacement of the amorphous doped layers with microcrystalline one is beneficial for both optical and electrical aspects which include a better Jsc when they are applied to the front, lower contact resistivity compared to amorphous layers and better FF thanks to the crystalline phase and the higher doping efficiency. Strikingly, hole collecting microcrystalline layer suppresses the transport barrier effect occurs at valance band offset, allowing a FF in the range of 70% at −100 °C while it is dropping to 40% for standard amorphous doped layers.

Energy Yield in Hot & Sunny Climates: Impact of Silicon Solar Cell Architecture and Cell Interconnection

Abstract: In this work, we investigate the temperature and irradiance dependencies of the power output of silicon solar cell architectures (BSF, PERC, PERT, SHJ). When we compare our data with commercial module datasheets, we find that the temperature coefficient under maximum power point conditions is systematically worse in the modules. Following our analysis we attribute this to ohmic losses $(R_{\mathrm{CTM}})$ due to cell interconnection. Using energy yield calculations we show the impact of $R_{\mathrm{CTM} }$ on the energy production in moderate and hot and sunny climates for all investigated architectures. We conclude that maximizing energy production in hot and sunny environments requires not only a high open-circuit voltage, but also a minimal series-to-Ioad-resistance ratio.