BEGIN:VCALENDAR VERSION:2.0 PRODID:Icfo X-PUBLISHED-TTL:P1W BEGIN:VEVENT UID:6a20a76ca62be DTSTART:20260618T140000Z SEQUENCE:0 TRANSP:OPAQUE LOCATION:ICFO Auditorium SUMMARY:ICFO | KARTIKA N. NIMJE CLASS:PUBLIC DESCRIPTION:Thermophotovoltaic (TPV) systems convert thermal radiation into electricity by coupling a hot emitter to a photovoltaic (PV) cell. Despit e important recent developments in the field\, TPV performance is ultimate ly constrained by a persistent power--efficiency trade-off: broadband radi ative exchange between an emitter and a cell yields high electrical power at the expense of efficiency\, whereas narrowband exchange leads to high e fficiency at the cost of reduced power. A more empirical way to express th is constraint is the difficulty of improving both the current and voltage characteristics of a cell simultaneously. Understanding the power--efficie ncy trade-off is therefore fundamental to optimizing TPV performance. This thesis develops a unified framework for understanding this trade-off and identifying photonic and electronic design strategies that enable optimal operation while remaining anchored to thermodynamic bounds.\nThe first par t of the thesis establishes the conceptual and quantitative backbone. A ph otonic view of thermal radiation connects Planck&rsquo\;s law and the Stef an--Boltzmann limit to the density of optical states\, coherence\, and sur face polaritons\, and clarifies the distinction between far-field and near -field exchange. These ideas are combined with the practical building bloc ks of TPVs &mdash\; spectral and angular emission control\, junction physi cs\, recombination\, and quantum efficiency &mdash\; to establish a practi cal design toolkit for TPVs. Within this toolkit\, detailed-balance and ra diative--thermodynamic analyses place TPVs on a power--efficiency landscap e bounded by Carnot and exergy (Landsberg) limits and identify spectral ba ndwidth as a central control knob governing performance.\nOn this foundati on\, the thesis explores three routes for mitigating the trade-off. First\ , hot-carrier TPVs introduce an internal thermodynamic degree of freedom b y treating the carrier subsystem as a reservoir with its own temperature a nd chemical potential and by harvesting carriers through energy-selective contacts\; in the ideal radiative limit\, this enables a single junction t o emulate multicolor performance and approach Carnot efficiency at finite power. Second\, an analytical framework for a near-field TPV system based on fluctuational electrodynamics derives analytical expressions for photon tunnelling between plasmonic and semiconducting media\, establishing scal ing laws that show how evanescent modes can deliver super-Planckian\, spec trally concentrated fluxes that support high power and high efficiency sim ultaneously. Third\, substrate engineering is shown to be instrumental in near-field TPV design: in an ITO/InAs case study\, optimizing thin\, low-l oss plasmonic films with tuned plasma frequency and thickness reshapes the tunnelling spectrum\, concentrating useful above-bandgap transfer while s uppressing sub-bandgap losses\, and shifts electrical power&ndash\;efficie ncy curves outward in the radiative limit.\nThis thesis reframes the TPV p ower--efficiency compromise as malleable rather than fixed: while the glob al thermodynamic frontiers are immutable\, the effective frontier accessib le to practical architectures can be steered through controlled interventi ons in spectra\, modes\, and carrier energetics. The analytical models\, t hermodynamic benchmarks\, and optimization strategies developed here provi de a principled basis for designing and evaluating TPV systems that combin e photonic control\, hot-carrier extraction\, and near-field coupling\, an d for assessing these theoretical results in relation to realistic materia l and device constraints.\n \;\nThesis Director: Prof. Dr. Georgia T. Papadakis DTSTAMP:20260603T221508Z END:VEVENT END:VCALENDAR