Group-III-nitride nanowires: electrical and optical properties in view of applications in solarcells

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Aim of the project E2 is the design of (In)GaN nanorod (NR) solarcells, exploring different cell concepts. Special care needs to be taken to doping of NRs, passivation of large surfaces and optimization of size, shape and assembly of NRs to obtain optimum absorption of sun light in as small as possible layer thicknesses. A careful control of optical and electronic properties of the NR ensembles embedded in additional dielectric layers, can be achieved based on feedback from optical, electrical and structural characterization of individual NRs as well as NRs in ensembles and relies on prior simulations and modeling of physical properties. Ultimately, the photovoltaic (PV) properties of the novel NR based materials will be determined using defined illumination (AM1.5) and will rely on the development of proper contacting schemes. For NR based composite materials optimization an intimate understanding of the interaction of NRs with their environment is crucial. In particular the following tasks/topics will be addressed: • interaction of NRs with organic molecules and inorganic passivation layers and the influence on Voc; • for a theoretical understanding of electronic defect states and atomistic defect structure at the NR/molecule or NR/passivation layer interfaces density functional theory calculations will be carried out in collaboration with partners; • interaction of NRs with incident light: optimization of size, shape and assembly of NRs with respect to optimum light absorption; simulation support to determine optimized light absorption using a three-dimensional full-wave vectorial finite element method (FEM); • interaction of NRs with absorption enhancing layers/structures such as quantum dot layers with high In content, transparent conductive oxide (TCO) layers, plasmonically active nanostructured metal layers, dielectric nanoparticle layers enhancing the light scattering and thus ultimately absorption in the NRs; • exploring the doping profile in NRs and its influence on electrical transport properties; • assessment of different NR based cell concepts involving radial or axial p-i-n junctions as well as semiconductor-insulator-semiconductor (SIS) cells that base on a tunneling junction or even heteroemitter structures that at present constitute the world record cell in silicon PV. All 6 tasks can only be performed in close collaboration between various partners in this collaborative research group, with a combination of their experimental, theoretical and technological expertise.