Radiative cooling to subambient temperatures can be efficiently achieved through spectrally selective emission, which until now has only been realized by using complex nanoengineered structures. Here, a simple dip-coated planar polymer emitter derived from polysilazane, which exhibits strong selective emissivity in the atmospheric transparency window of 8–13 μm, is demonstrated. The 5 μm thin silicon oxycarbonitride coating has an emissivity of 0.86 in this spectral range because of alignment of the frequencies of bond vibrations arising from the polymer. Furthermore, atmospheric heat absorption is suppressed due to its low emissivity outside the atmospheric transparency window. The reported structure with the highly transparent polymer and underlying silver mirror reflects 97% of the incoming solar irradiation. A temperature reduction of 6.8 °C below ambient temperature was achieved by the structure under direct sunlight, yielding a cooling power of 93.7 W m–2. The structural simplicity, durability, easy applicability, and high selectivity make polysilazane a unique emitter for efficient prospective passive daytime radiative cooling structures.

solar, wind, hydro, geothermal, and biomass, to enable a steady mitigation of greenhouse gas emissions, which are causing the planetary climate change and global warming. [5][6][7] Additionally, due to the economic development and the worldwide urbanization, a continuous rise of the global energy consumption across all key sectors, that is, power, heating, industry, and transport is occurring. This is expressed by an increase in the annual global electricity demand by 4.5% in 2021 corresponding to additional 1000 TWh. [4] Hence, strict criteria for the selection of competitive and abundant energy alternatives are imposed, requiring high yield at affordable prices. [8] The share of total renewables power generation excluding hydropower exceeded 3000 TWh in 2020, corresponding to almost 12% of the global electricity generation. [3] Considering an effective synergy between various sustainable energy candidates, solar photovoltaics (PV) have demonstrated great capabilities that can satisfy the requirements in the pathway towards 100% renewable electricity. [9][10][11][12] Owing to the research and development activities over the last decades, the power conversion efficiencies of solar cells (SC) have skyrocketed with a prolonged operation lifetime (>15 years) and a drastic plummeting in manufacturing costs (global average module selling price below $0.25 per W). [6,[13][14][15] The rapid universal deployment of PV resulted in a contribution of about 3.4% in the worldwide electricity generation in 2020. [3] Presently, the global installed PV capacity is approaching 1 TW and it is envisioned to reach ≈10 TW by 2030 and 30 to 70 TW by 2050. [16] Interestingly, along with massive electricity production using conventional solar power plants and rooftop solar panels, ancillary concepts of PV offer new strategies for supplying modern systems in versatile applications. [17][18][19] Moreover, diverse functionalities beyond solar energy harvesting can be afforded by adaptive PV, including aesthetic appearance, visual comfort and thermal management. [17,18,20,21] The distributed nature and the ubiquitous accessibility of multifunctional PV products are substantial features of solar PV in contrast to other renewable energies. However, traditional SCs dominating the market impose intrinsic optoelectronic and thermomechanical limitations, that prohibit their multifunctional utilization. To overcome these drawbacks, novel functional materials and innovative device architecture Solar photovoltaics (PV) offer viable and sustainable solutions to satisfy the growing energy demand and to meet the pressing climate targets. The deployment of conventional PV technologies is one of the major contributors of the ongoing energy transition in electricity power sector. However, the diversity of PV paradigms can open different opportunities for supplying modern systems in a wide range of terrestrial, marine, and aerospace applications. Such ubiquitous and versatile applications necessitate the development of PV technologies with customized desig...

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In recent years, the German Aerospace Center (DLR) developed Gossamer deployment systems in different projects. As power requirements of spacecraft are getting more and more demanding, DLR recently focused on the development of new deployable photovoltaic (PV) technologies that are suitable for generating 10’s of kW per array. Possible space applications that may also require high power supply are missions using electric propulsion such as interplanetary missions, placing of geostationary (GEO) satellites in their orbit or even more future oriented as space tugs or lightweight power generation on extra-terrestrial infrastructures. The paper gives an overview about a feasibility study for flexible solar arrays based on new thin-film photovoltaics. It is expected that the combination of new thin-film PV technologies, e.g., copper indium gallium selenide (CIGS) cells or gallium–arsenide (GaAs) cells, together with Gossamer deployment technologies, could significantly increase the power availability for spacecraft. Based on a requirement, analysis system concepts were evaluated. A focus is on the potential of CIGS PV combined with a two-dimensional deployment of the array and DLR’s coilable carbon fibre-reinforced plastic (CFRP) booms. Therefore, a concept based on crossed booms with a foldable PV membrane is considered as baseline for further developments. The array consists of rectangular PV generators that are interconnected by flexible printed circuit board (PCB) harness. By a double-folding technique, these generators are laid on top of each other in such that the membrane can be extracted from its stowing box during the deployment in a controlled manner. Considering constantly increasing efficiencies of the CIGS PV combined with Gossamer structures, there is clear potential of reaching a very high specific power value exceeding that of conventional PV systems. Furthermore, the CIGS PV appears to be more radiation resistant and has already reached more than 21% efficiency in laboratories. Such efficiencies are expected to be achieved in the near future in a standard manufacturing process. However, flexible, thin-film GaAs cells are also subject of consideration within GoSolAr. With this prospect, DLR’s research has the goal to develop a Gossamer Solar Array (GoSolAr) to exploit the described potential.