Ultra-thin solar cells are a nascent photovoltaic strategy that holds ample advantages compared to conventional thick technologies, spanning from cost and material savings to low weight and flexibility. Solar cells on this length-scale also exhibit intrinsic tolerance to radiation damage, thus being uniquely suited for space power applications. Despite this breadth of compelling characteristics, poor solar energy harvesting remains a fundamental challenge for the advancement of ultra-thin solar cells, as device thickness is intrinsically related to the efficiency of sunlight absorption and power generation.

Maximising the absorption of sunlight in ultra-thin solar cells requires careful optimisation of the full device design, tailored to minimise i) front surface reflection by means of antireflection coatings, ii) transmission losses into the substrate by means of a rear mirror, and iii) outcoupling losses by means of light-trapping textures. Simultaneous application of these strategies, within architectures possessing maximal transparency outside the active region, is imperative to target competitive photovoltaic efficiencies on such reduced length-scales.

In this thesis I investigate viable platforms to achieve optimal and holistic light management in ultra-thin solar cells. I give particular attention to the development of advanced light-trapping strategies, concentrating on texture designs to exploit waveguide resonances as absorption enhancement mechanisms. For this purpose, I build a robust framework to study waveguide modes in ultra-thin devices with integrated textures. Based on this framework, comprehensive computational investigations unravel design-driven mechanisms to regulate the light-harvesting potential of these optical modes. My studies escalate into the development of novel light-trapping platforms beyond current paradigms, where the full texture design is tailored to mold its scattering profile together with the modal structure of its host device, allowing engineering of their overlap and unlocking superior waveguiding benefits. Ultimately, my investigations culminate in the identification of light-trapping designs that forecast remarkable 20% photovoltaic efficiency in an 80 nm GaAs cell. Such outstanding potential is supported by the experimental validation of computational techniques, as well as the demonstration of feasible fabrication approaches for the integration of favourable texture designs. Overall, the work presented herein provides fundamental and practical insights for the advancement of ever-thinner photovoltaic technologies.