BEGIN:VCALENDAR VERSION:2.0 PRODID:Icfo X-PUBLISHED-TTL:P1W BEGIN:VEVENT UID:69d4b430b0c66 DTSTART:20241129T100000Z SEQUENCE:0 TRANSP:OPAQUE DTEND:20241129T110000Z LOCATION:Elements Room SUMMARY:ICFO | FRANCISCO GUMARO BERNAL TEXCA CLASS:PUBLIC DESCRIPTION:The large dependence on fossil fuels led to a severe environmen tal crisis\, evident in the acceleration of climate change caused by the g reenhouse effect. This unsustainable model has led to a reassessment of ou r energy infrastructure\, which has initiated a shift towards more sustain able energy sources. Renewable energy sources\, such as wind\, hydro\, and particularly solar\, provide a more sustainable alternative. Solar energy \, which can be transformed into electrical energy by photovoltaic (PV) ce lls\, is notable for its abundant availability and minimal environmental i mpact. However\, intrinsic fundamental losses in solar energy conversion l imit the power conversion efficiency (PCE) of single-junction planar geome try solar cell devices to 33.1%\, as described by the Shockley-Queisser de tailed balance model. In this thesis\, we address the study of two fundame ntal losses limiting the maximum efficiency achievable by planar-geometry single-junction solar cells. We consider the approach on organic solar cel l (OSC)s because they offer significant benefits over traditional inorgani c-based cells. OSCs\, made from carbon-based materials\, can be flexible\, integrable\, lightweight\, and potentially less costly to produce. These qualities make OSCs a promising innovation for incorporating solar power i nto a wider range of applications\, advancing the pursuit of a cleaner\, m ore sustainable energy future. The thesis is organized into four main chap ters. In Chapter 1 we discuss global energy demand and positioning solar e nergy as a sustainable alternative. It also covers a discussion on the int rinsic losses leading to the fundamental limits in solar energy conversion . Chapter 1 also provides an overview of the state-of-the-art OSCs\, inclu ding the properties of organic semiconductor materials and device photophy sics\, and concludes with a justification for the research developed and d escribed in the rest of the thesis. Chapter 2 focuses on mitigating transm ission and thermalization losses by employing a tandem strategy. To overco me some of the limitations of the two-terminal configuration\, we develop a four-terminal tandem structure composed of a transparent front and an op aque back cell\, thus enhancing fabrication feasibility and overall perfor mance. Chapters 3 and 4 delve into Boltzmann losses linked to a mismatch b etween the absorption and emission cones that directly impact the maximum achievable open-circuit voltage (Voc). In Chapter 3\, we investigate the m echanisms governing the quasi-Fermi level splitting (QFLS) dynamics in OSC s. Our study identifies direct radiative recombination and recombination v ia trapping states as the two primary competing processes controlling the QFLS in PM6:Y6 solar cells. We propose a strategy to passivate trap states \, leading to a reduction in mid-gap trap states density and\, consequentl y\, an increase in Voc. We highlight the role played by radiative recombin ation in regulating the final Voc of such PM6:Y6 solar cell. Chapter 4 bui lds on these findings by leveraging the emitted photons to experimentally demonstrate an Voc enhancement through the restriction of photon emission\ , thereby reducing Boltzmann losses. We demonstrate that using a two-optic al resonance cavity configuration\, we can obtain a reduction in the misma tch between the absorption and emission cones in OSCs. We experimentally d emonstrate a solely optical-based Voc increase larger than 30 mV. In summa ry\, the findings in the present thesis establish an optical-based path to increase Voc and the performance of the solar cells and eventually surpas s the Shockley-Queisser PCE limit for planar-geometry single-junction sola r cells.\n \;\nFriday November 29\, 11:00 h. ICFO Elements Room \nThes is Director: Prof. Dr. Jordi Martorell DTSTAMP:20260407T073720Z END:VEVENT END:VCALENDAR