Ultrathin Nano-Absorbers in Photovoltaics: Prospects and Innovative Applications

Approaching the first terawatt of installations, photovoltaics (PV) are about to become the major source of electric power until the mid-century. The technology has proven to be long lasting and very versatile and today PV modules can be found in numerous applications. This is a great success of the entire community, but taking future growth for granted might be dangerous. Scientists have recently started to call for accelerated innovation and cost reduction. Here, we show how ultrathin absorber layers, only a few nanometers in thickness, together with strong light confinement can be used to address new applications for photovoltaics. We review the basics of this new type of solar cell and point out the requirements to the absorber layer material by optical simulation. Furthermore, we discuss innovative applications, which make use of the unique optical properties of the nano absorber solar cell architecture, such as spectrally selective PV and switchable photovoltaic windows

Amorphous single-junction cells for vertical BIPV application with high bifaciality

Solar cells used in building integration of photovoltaic cells (BIPV) are commonly made from crystalline wafer cells. This contribution investigates the challenges and benefits of using bifacial solar cells in vertical installations. We show that those cells get up to 13% more irradiance compared to optimum tilted south facing monofacial modules in Germany. The role of the n-layer in thin amorphous bifacial single-junction cells intended to be used as bifacial cells in BIPV applications is investigated. In contrast to the superstrate cell design, a transparent n-layer and back contact play a key role to achieve high bifaciality. We therefore increased the transparency of the n-layer by adding CO2, increasing the PH3 flow in the deposition gas and tested different thicknesses. With those measures, we reached a bifaciality of 98% for short-circuit current density and 99% for open-circuit voltage

Optical design and bandgap engineering in ultrathin multiple quantum well solar cell featuring photonic nanocavity

Ultrathin solar cells are efficient and captivating devices with unique technological and scientific features in terms of minimal material consumption, fast fabrication processes, and good compatibility with semi-transparent applications. Such photovoltaic (PV) technologies can enable effective synergy between optical and electronic confinements with large tuning capabilities of all the optoelectronic characteristics. In this work, the implications of the optical design and the bandgap engineering in ultrathin hydrogenated amorphous Si/Ge multiple quantum well (MQW) solar cells featuring photonic nanocavity are analyzed based on experimental measurements and optoelectronic modelling. By changing the period thicknesses and the positions of QWs inside the deep-subwavelength nanophotonic resonator, the spatial and spectral distributions of the optical field and the local absorption are strongly affected. This leads to a modulation of the absorption resonance condition, the absorption edge and the resulting photocurrent outputs. Because of quantum confinement effect, the change of MQW configurations with different individual QW periods while keeping similar total thickness of about 20 nm alters both the bandgap energy and the band offset at the QW/barrier heterojunctions. This in turn controls the photovoltage as well as the carrier collection efficiency in solar cells. The highest open circuit voltage and fill factor values are achieved by employing MQW device configuration with 2.5 nm-thin QWs. A record efficiency above 5.5% is reached for such emerging ultrathin Si/Ge MQW solar cell technology using thinner QWs with sufficient number, because of the optimum trade-off between all the optoelectronic characteristic outputs. The presented design rules for opaque ultrathin solar cells with quantum-confined nanostructures integrated in a photonic nanocavity can be generalized for the engineering of relevant multifunctional semitransparent PV devices

Exploring the Feasibility of Battery Electric and Fuel Cell Electric Vehicles as Peaker Plant Substitutes at Low Wind and Irradiation Conditions

In this paper a comparison between the use of Battery Electric Vehicles (BEVs) and Fuel Cell Electric Vehicles (FCEVs) to span cold dark doldrums (“Dunkelflaute”) in a future energy system with a high penetration of renewable energy supply is presented. A big problem with the cold dark doldrums is the rareness of the situation. Any power plant built to specifically be used during those special weather conditions will be operated only 0.1 % of the time according to a study on the energy demand in Germany in 2050 Aurora (2021) even though 10 GW are required to meet the demand. A prototype FCEV docking station to measure power transfer efficiencies was built. By this, we investigated supplying a district with energy via FCEVs by simulating a district with varying amounts of BEVs present. It is possible to supply a district with a low number of FCEVs although a stationary hydrogen connection would be beneficial. The efficient transfer of energy from a FCEV to a building requires a careful design of the plate heat exchangers and depends on the temperature level of the supplied building

Fuel Cell Electrical Vehicles as Mobile Coupled Heat and Power Backup-Plant in Neighbourhoods

Fuel cell electric vehicles (FCEVs) can be used during idle times to convert hydrogen into electricity in a decentralised manner, thus ensuring a completely renewable energy supply. In addition to the electric power, waste heat is generated in the fuel cell stack that can also be used. This paper investigates how the energy demand of a compiled German neighbourhood can be met by FCEVs and identifies potential technical problems. For this purpose, energy scenarios are modelled in the Open Energy System Modelling Framework (oemof). An optimisation simulation finds the most energetically favourable solution for the 10-day period under consideration. Up to 49% of the heat demand for heating and hot water can be covered directly by the waste heat of the FCEVs. As the number of battery electric vehicles (BEVs) to be charged increases, so does this share. 5 of the 252 residents must permanently provide an FCEV to supply the neighbourhood. The amount of hydrogen required was identified as a problem. If the vehicles cannot be supplied with hydrogen in a stationary way, 15 times more vehicles are needed than required in terms of performance due to the energy demand

Ultrathin Solar Cell With Magnesium-Based Optical Switching for Window Applications

Photovoltaic windows that can be switched between transparent and energy harvesting mode can be realized by using ultrathin solar absorbers embedded in an optical nanocavity. In the present work, we use a 5 nm thick amorphous germanium absorber integrated in a magnesium-based thin film optical cavity, which switches from an absorptive to a transparent state due to hydrogen absorption. We analyze the influence of the mirror layer thickness on the light absorption, photocurrent generation, and transmission as well as color neutrality of the device. The optical properties are studied by 1-D transfer-matrix method by changing Mg thickness between 0 and 100 nm, then compared to the experimental results of fabricated devices. When the thickness of Mg increases, the switchable average transparency varies between 25% and 0%, while the power conversion efficiency rises up to 2.3%. The applicability of the device is tested by modeling the annual power generation in realistic scenarios. The influence of the cardinal orientation and the seasons on the switchable photovoltaic window implemented in a building facade with the abovementioned parameters is analyzed for different switching scenarios

Simulative Evaluation Of High Temperature Versus Low Temperature Heating Networks To Utilise Waste Heat From Large Fuel Cells For Powering Districts

Fuel cells generate heat as byproduct which can be used for space heating. In heavy duty fuel cells, this waste heat can potentially be used for district heating during times of low renewable generation and high demand

A vapor-phase-assisted growth route for large-scale uniform deposition of MoS2 monolayer films

In this work a vapor-phase-assisted approach for the synthesis of monolayer MoS2 is demonstrated, based on the sulfurization of thin MoO3−x precursor films in an H2S atmosphere. We discuss the co-existence of various possible growth mechanisms, involving solid–gas and vapor–gas reactions. Different sequences were applied in order to control the growth mechanism and to obtain monolayer films. These variations include the sample temperature and a time delay for the injection of H2S into the reaction chamber. The optimized combination allows for tuning the process route towards the potentially more favorable vapor–gas reactions, leading to an improved material distribution on the substrate surface. Raman and photoluminescence (PL) spectroscopy confirm the formation of ultrathin MoS2 films on SiO2/Si substrates with a narrow thickness distribution in the monolayer range on length scales of a few millimeters. Best results are achieved in a temperature range of 950–1000 °C showing improved uniformity in terms of Raman and PL line shapes. The obtained films exhibit a PL yield similar to mechanically exfoliated monolayer flakes, demonstrating the high optical quality of the prepared layers

GIS-based technical analysis of the local renewable energy production potentials of farms in Germany

This study evaluates the potential for integrating renewable energy on farms in Germany. Using Geographic Information Systems, the research assesses the spatial distribution of potential locations for renewable power plants, considering various datasets associated with animal husbandry, existing power plants, farm locations, and meteorological conditions. The analysis reveals potential for small-scale wind and photovoltaic power plants. In particular, the potential for small-scale wind power plants is approximately 4 TWh/a, concentrated mainly in the northern regions of Germany. For photovoltaic power plants, the total potential is estimated at around 637 TWh/a, with a distribution of 56 % for ground-mounted systems, 37 % for agrivoltaic systems, and 7 % for rooftop photovoltaics. The distribution of photovoltaic systems indicates, that ground-mounted systems are predominantly located in the eastern part, rooftop systems in the northwest, and agrivoltaics in Rhineland-Palatine and Baden-Württemberg. The study also identifies near surface geothermal potential in the northwest, Molasse, and Rhine basins. The overview provides valuable insights into optimal locations for sustainable energy production for farmers