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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Oxide/metal/oxide (OMO) layer stacks are used to replace transparent conductive oxides as front contact of thin-film solar cells. These multilayer structures not only reduce the overall thickness of the contact, but can be used for colouring of the cells utilizing interference effects. However, sheet resistance and parasitic absorption, both of which depend heavily on the metal layer, should be further reduced to reach higher efficiencies in the solar cells. In this publication, AgOX wetting layers were applied to OMO electrodes to improve the performance of Cu(In,Ga)Se2 (CIGS) thin-film solar cells. We show that an AgOX wetting layer is an effective measure to increase transmission and conductivity of the multilayer electrode. With the presented approach, we were able to improve the short-circuit current density by 18% from 28.8 to 33.9 mA/cm2 with a metal (Ag) film thickness as low as 6 nm. Our results highlight that OMO electrodes can be an effective replacement for conventional transparent conductive oxides like aluminium-doped zinc oxide on thin-film solar cells.

Photovoltaic windows that can be switched between 4 transparent and energy harvesting mode can be realized by using 5 ultrathin solar absorbers embedded in an optical nanocavity. In the 6 present work, we use a 5 nm thick amorphous germanium absorber 7 integrated in a magnesium-based thin film optical cavity, which 8 switches from an absorptive to a transparent state due to hydrogen 9 absorption. We analyze the influence of the mirror layer thickness 10 on the light absorption, photocurrent generation, and transmission 11 as well as color neutrality of the device. The optical properties are 12 studied by 1-D transfer-matrix method by changing Mg thickness 13 between 0 and 100 nm, then compared to the experimental results of 14 fabricated devices. When the thickness of Mg increases, the switch-15 able average transparency varies between 25% and 0%, while the 16 power conversion efficiency rises up to 2.3%. The applicability of 17 the device is tested by modeling the annual power generation in 18 realistic scenarios. The influence of the cardinal orientation and 19 the seasons on the switchable photovoltaic window implemented in 20 a building facade with the abovementioned parameters is analyzed 21 for different switching scenarios. 22 Index Terms-Magnesium optical switching, smart window, 23 switchable solar cell, ultrathin solar cell. 24 I. INTRODUCTION 25 I N MODERN buildings, huge glass facades often separate the 26 interior from the exterior environment. They are supposed to 27 supply thermal and visual comfort to the inner of the building. 28 To improve this comfort, shading systems have to be imple-29 mented, which provide effective light and heat management 30 [1]-[3]. Dynamic daylight control can be provided by smart 31 windows, which attracted great interest in recent years [4]-[8]. 32 These windows are able to reduce the amount of energy needed 33 for cooling in the building [9]. The emergence of switchable Q1 34 solar cells added a new energy harvesting capability to these 35 smart windows. While still being able to dynamically block 36 sunlight from entering the interior of a building, these smart 37 solar windows generate electricity at the same time. For the 38 realization of a smart photovoltaic window, a technical solution 39 enabling reversible switching from a transparent state to an ab-40 sorbing photovoltaic state is required. Different approaches are 41 523