Crystalline silicon (c-Si) is one of the best candidates to develop transparent solar cells with high efficiency and stability because conventional c-Si solar cells are known to exhibit high efficiency and long-term stability compared with other solar cells. However, the opaque characteristic of the c-Si wafer hinders the development of transparent solar cells using c-Si. In this presentation, I will introduce a novel approach to developing neutral-colored transparent c-Si solar cells that exhibit the highest efficiency among neutral-colored transparent solar cells developed to date.

This talk highlights two parallel technologies developed in my lab for solar energy harvesting. First, femtosecond lasers are utilized for material processing and functionalization, which enabled the creation of the so-called black and colored metals. Here, I will discuss the black and colored metals in a range of photo-thermal applications. Second, I will discuss our recent push in introducing a pure physics-based approach to enhance perovskite performance by utilizing metamaterials. This physics approach rivals the most advanced chemical engineering and provides a new pathway for enhancing perovskites' performance in photo-voltaic applications.

Layers of organic molecules are capable of generating multiple excitons per absorbed photon though a process known as singlet fission. As such, this process could be employed to fabricate a solar cell which circumvents the efficiency limits imposed by a single threshold design. Leveraging experience with silicon solar cells, the OMEGA Si project is developing a device that combines the maturity and high efficiency of crystalline silicon with the exciton multiplication afforded by singlet fission. This talk will communicate progress of the project including experiments to elucidate exciton and carrier transfer between the singlet fission layer and the underlying silicon solar cell.

Passive radiative cooling technology offers viable solution for the thermal management of both buildings and photovoltaics (PV) sectors in terrestrial and extraterrestrial applications. Herein, we demonstrate and analyze the effectiveness of a simple solution-processed thin organopolysilazane polymer coating as thermal emitter for sub-ambient passive daytime radiative cooling (PDRC) of surface structures and solar cell devices. The 5µm thick Siliconoxycarbonitride (SiCNO) polymer emitter features spectral selective emissivity in Mid-Infrared spectrum due to the perfect overlap of the vibrational modes of Si-O-Si, Si-N-Si, Si-C bonds with the atmospheric transmittance window. Applying the SiCNO emitter on a metallic reflector substrate yields high reflection in the solar wavelength range (0.3-2.5µm), and high narrowband emissivity in the atmospheric transmittance window (8-13 μm). The thin PDRC device can cool down to 6.8°C below ambient corresponding to a net cooling power of 93.7 W/m2. The deep sub-ambient cooling performance of PDRC was experimentally demonstrated using a cryogenic indoor setup under vacuum conditions reaching a max ∆T of 33°C (at 10-3 Pa) below ambient. Using analytical modeling we studied the impact of individual parasitic heat losses on the PDRC under variable air pressure. We suggest a rational design of sub-components and operational pressure regimes for a vacuum-based cooler system in real-world applications. Moreover, the SiCNO coating is a suitable candidate as an encapsulating coating for solar modules due to the exceptionally high transmissivity in the solar spectrum range and high emissivity in the infrared region. Our thermal and electrical analysis demonstrated that the polymer emitter can solitarily cool down lightweight flexible solar modules in a lower earth orbit by 30°C without inducing efficiency losses from the device. The robustness of this hydrophobic protective polymer coating was proven through various accelerated degradation tests. The results from these investigations indicate that polysilazane polymer coating is an excellent thermal emitter material for both terrestrial and space applications.

The thermoradiative diode (TRD) is the symmetric counterpart to the photovoltaic solar cell that generates power via the net emission rather than absorption of light. While the TRD has enticing applications in night-sky power generation, there are also opportunities for power generation via waste heat recovery. However, while the theoretical limits for power generation are promising, the current technological limits have not been explored. Here we compare the electro-optical characteristics of HgCdTe photodiodes in operating in both thermoradiative and thermophotovoltaic (TPV) modes, supported by optical modelling. By contrasting thermoradiative and TPV operation using the same devices, we set realistic expectations for power generation using mid-infrared semiconductors.

Thermophotovoltaics and thermal barrier coatings both require resilient materials capable of surviving extremely high temperatures associated with their applications. To obtain higher performance, it is also important that they have the ability to retain nanostructural integrity through large temperature swings. In this work, we present several concepts for achieving this goal, along with our initial characterization data demonstrating the value of this effort.

In thermophotovoltaics, photovoltaic cells convert heat from a thermal emitter to electricity. One way to obtain high-efficiency devices is to tailor the emitted spectrum to a specific solar cell. Here, we propose to use ultra-thin films to tailor the emission of hot bodies, where we can control the emission spectrum through material choice and film thickness. We predict power conversion efficiencies >50%, and suggest new material systems for exploration with potential efficiencies >60%. Our concept is universal and can be expanded to other high-temperature photonic applications for spectral control of thermal emission.