The author is mainly responsible for this work. The author developed the idea, designed & conducted the experiments and measurements, and analysed the data. The author was responsible for writing the manuscript, communicating with the journal editor and answering to the reviewers' queries. Publication 2: Enhanced efficiency of hybrid amorphous silicon solar cells based on single-walled carbon nanotubes and polymer composite thin film. The author is mainly responsible for this work. The author designed & conducted the experiments, fabricated & measured the devices, and analysed the data. The author was responsible for writing the manuscript, communicating with the journal editor, and answering to the reviewers' questions. Publication 3: Synergistic Effect of Single-Walled Carbon Nanotubes and PEDOT:PSS in Thin Film Amorphous Silicon Hybrid Solar Cell. The author is mainly responsible for conceptualization of the idea, design of experiments, measurements, data analysis, and jointly writing the paper. The author was responsible for answering to the reviewers' questions. Publication 4: Rational design of highly efficient flexible and transparent ptype composite electrode based on single-walled carbon nanotubes. The author is mainly responsible for this work. The author designed & conducted the experiments, fabricated & measured the devices, and analysed the data. The author was responsible for writing the manuscript, and answering to the reviewers' questions. Publication 5: Review: Hybrid heterojunction solar cells based on singlewalled carbon nanotube and amorphous silicon thin films. The author is mainly responsible for this work and writing the paper.

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.

An optical study based on spectroscopic ellipsometry, performed on ultrathin hydrogenated amorphous silicon (a-Si:H) layers, is presented in this work. Ultrathin layers of intrinsic amorphous silicon have been deposited on n-type mono-crystalline silicon (c-Si) wafers by plasma enhanced chemical vapor deposition (PECVD). The layer thicknesses along with their optical properties –including their refractive index and optical loss- were characterized by spectroscopic ellipsometry (SE) in a wavelength range from 250 nm to 850 nm. The data was fitted to a Tauc-Lorentz optical model and the fitting parameters were extracted and used to compute the refractive index, extinction coefficient and optical bandgap. Furthermore, the a-Si:H film grown on silicon was etched at a controlled rate using a TMAH solution prepared at room temperature. The optical properties along with the Tauc-Lorentz fitting parameters were extracted from the model as the film thickness was reduced. The etch rate for ultrathin a-Si:H layers in TMAH at room temperature was found to slow down drastically as the c-Si interface is approached. From the Tauc-Lorentz parameters obtained from SE, it was found that the a-Si film exhibited properties that evolved with thickness suggesting that the deposited film is non-homogeneous across its depth. It was also found that the degree of crystallinity and optical (Tauc) bandgap increased as the layers were reduced in thickness and coming closer to the c-Si substrate interface, suggesting the presence of nano-structured clusters mixed into the amorphous phase for the region close to the crystalline silicon substrate. Further results from Atomic Force Microscopy and Transmission Electron Microscopy confirmed the presence of an interfacial transitional layer between the amorphous film and the underlying substrate showing silicon nano-crystalline enclosures that can lead to quantum confinement effects. Quantum confinement is suggested to be the cause of the observed increase in the optical bandgap of a-Si:H films close to the a-Si:H/cSi interface.

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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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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