Buildings are responsible for over 40% of total primary energy consumption in the US and EU and therefore improving building energy efficiency has significant potential for obtaining net-zero energy buildings reducing energy consumption. The concurrent demands of environmental comfort and the need to improve energy efficiency for both new and existing buildings have motivated research into finding solutions for the regulation of incoming solar radiation, as well as ensuring occupant thermal and visual comfort whilst generating energy onsite. Windows as building components offer the opportunity of addressing these issues in buildings. Building integration of photovoltaics permits building components such as semi-transparent façade, skylights and shading devices to be replaced with PV. Much progress has been made in photovoltaic material science, where smart window development has evolved in areas such as semi-transparent PV, electrochromic and thermochromic materials, luminescent solar concentrator and the integration of each of the latter technologies to buildings, specifically windows. This paper presents a review on intelligent window technologies that integrate renewable energy technologies with energy- saving strategies contributing potential solutions towards sustainable zero-energy buildings. This review is a comprehensive evaluation of intelligent windows focusing on state-of-the-art development in windows that can generate electricity and their electrical, thermal and optical characteristics. This review provides a summary of current work in intelligent window design for energy generation and gives recommendations for further research opportunities.

Windows integrated with semi-transparent photovoltaics (PVs) such as Dye-Sensitized Solar Cells (DSSCs) show good potential in improving building performance, in terms of providing daylight, reducing unnecessary solar heat gain and also generating electricity onsite. However, low cell efficiency remains an obstacle for their applications in windows. Using light trapping structures in DSSCs shows the potential to improve solar to electrical conversion efficiency. In this work, different pyramid-patterned titanium dioxide (TiO₂) geometries are designed to enhance the photon absorption in DSSCs, and characterised using a Monte-Carlo algorithm based 3D ray-tracing simulation. Various studies were carried out under average irradiation, spectrum dependent irradiation and different solar incidental angles, respectively. The simulation results at the average irradiation wavelength (540 nm) were compared to those from a previous study using Scanning Photocurrent Microscopy (SPCM) and a reasonable agreement has been achieved. It was found that the structure based on the pyramid array of side wall angle 54.7° can significantly enhance light absorption by up to ~25% and the maximum achievable photocurrent density (MAPD) by up to ~45% across the spectrum of 380–800 nm, when compared to a planar control counterpart.