Solar Canvas: Nanoscale light management for ultra-thin, semi-transparent, and colourful solar cells

This thesis provides new solutions for integrable PV by exploiting nanophotonic principles in nanoscale architectures. It shows a high degree of control over the absorption/transmission spectrum by using optical waveguiding in either nanowires (NW) or thin films. In Chapter 2, we focus on understanding the optical properties of vertically standing semiconductor NWs as promising building blocks for next generation photonics and photovoltaics. In Chapter 3, we explore in detail the potential of semiconductor NW-based solar cells as a powerful and tunable-in-design approach for wavelength-selective semi-transparent solar cells for BIPV. Optical simulations and experimental demonstration of PMDS-embedded NW arrays confirm that by changing diameter and periodicity one can engineer the absorption and transmission spectra of the NW array to provide a broad range of bright colours, semi-transparency and high PV performance. Chapter 4 focuses on ultrathin, high efficiency and flexible Si solar cells as another photonic-based solution to minimize the compromise of high conversion efficiency for aesthetics in solar cells. Here we present a new family of surface texturing, based on correlated disordered hyperuniform patterns, capable of manipulating scattering spectrum of the incident light to be efficiently coupled into the silicon slab optical modes. We experimentally demonstrate 66.5% solar light absorption in free-standing 1um c-Si layers by using these nanotextures. Finally, in Chapter 5, we combine the unique light waveguiding and absorption in vertically standing NWs with k-space engineering given by their arrangement into arrays to increase absorption in an ultra-thin tandem cell beyond the bulk limits. The photonic and design concepts presented here combined with highly-performing PV materials make the intersection between high-efficiency, flexibility, colour-tunability and transparency closer to reality.