Photovoltaic energy conversion is the sustainable source of the present and of the future. In the last two decades, its deployment increased by several orders of magnitude, and will keep increasing as solar cell prices keep decreasing. Silicon currently dominates the PV market, but a next generation technology is needed to keep pushing prices down and increasing efficiency. CIGS solar cells are lighter, flexible, and already cheaper to produce than silicon, but their performance is still limited. Nanowires can help improve both cost and efficiency thanks to reduced material consumption, and intrinsically higher performance. In this project we aim to deposit periodic arrays of isolated nanowires by MBE, and by optimising their passivation as well as developing a novel device structure, we hope to increase the efficiency of CIGS solar cells. To do so, we will combine the expertise of the applicant in the growth of III-V semiconductor thin film and nanowires with the knowledge of the host in CIGS materials and MBE, using advanced characterisation techniques and state-of-the-art fabrication facilities.