Single Junction and Tandem Junction Nanowire Solar Cells

Sammanfattning: Solar cells based on silicon are successfully harvesting solar energy in established and increasingly widespread solar panels. However, their efficiency is limited by the Shockley–Queisser limit. For certain applications where high efficiency is the key figure of merit, the use of multi-junction solar cells is desirable.III–V multi-junction solar cells exhibit the highest efficiencies achieved to date, but suffer from the high cost of the III–V materials.Arrays of III–V nanowires show strong light absorption while covering only a small fraction of the surface, minimizing materials consumption. Therefore, solar cells made from III–V nanowire arrays are a possible candidate to achieve high efficiencies at a fraction of the cost of traditional planar III–V solar cells. This thesis aims to contribute to the development of III–V nanowire solar cells by addressing some of the challenges the technology is facing.Concerning single junction nanowire solar cells, Paper I investigates the effects of the device size on the performance. In contrast to the commonly used devices in nanowire solar cell research with an area below 1×1mm2, significantly larger devices with an area of 10×10 mm² were processed, and the effects of device size on the external quantum efficiency (EQE) and J–V characteristics are investigated.A concept of optically transparent nanowire solar cells which can absorb near-infrared radiation is presented in Paper II.In the realm of nanowire synthesis, Paper III is a comparative study of two different Ga precursors to establish favorable conditions for the growth of GaInP nanowire segments. Paper IV reports on the successful processing of tandem junction nanowire solar cells based on a GaInP top junction and an InP bottom junction, connected by an Esaki tunnel diode.