EXTENSIBLE MODELLING FRAMEWORK FOR NANOSTRUCTURED III-V SOLAR CELLS Markus F Führer 1 , Jessica GJ Adams 1 , Keith WJ Barnham 1 , Ben C Browne 1 , Ngai LA Chan 1 , Daniel J Farrell 1 , Louise Hirst 1 , Kan-Hua Lee 1 , Ned J Ekins-Daukes 1 , Akio Ogura 2 , Katsuhisa Yoshida 2 , Yoshitaka Okada 2 1 Imperial College London, London, United Kingdom 2 Research Center for Advanced Science and Technology, The University of Tokyo, Tokyo, Japan ABSTRACT The use of nanostructures has been shown to provide practical performance enhancements to high-efficiency III- V based solar cells by permitting sub-bandgap tuneable absorption. Nanostructures present a fertile ground for new solar cell technologies, and an improved understanding of fundamental processes may even lead to functional intermediate band and hot-carrier devices. As the fundamental processes occurring in nanostructured solar cells are complex and not easily observable, the study of such devices often requires the analysis of data derived from experimental characterisation techniques using computer models. Models exist for many individual aspects of these nanostructured solar cells, but as yet no comprehensive modelling solution exists. We report on our progress to produce an extendable abstract modelling framework written in the high-level programming language Python. The framework is intended for deployment both as back-end to a variety of interfaces for specialised modelling purposes, and as a library of methods and classes for use at source-code level, allowing adaptation to a wide variety of research problems. Significant code abstraction, such as sequestering complex materials parameterisation behind a simple material object allows simple scripts to do complex work. Modules underway cover several device simulation tiers, including fundamental processes such as quantum well and dot absorption and recombination, as well as device level simulations such as spatial bias mapping using equivalent circuits and multijunction IV characteristics. These simulations correlate with and derive experimental data from characterisation techniques including spatially and temporally resolved electro- and photoluminescence spectroscopy, fourier-transform infrared spectroscopy, and others. NANOSTRUCTURED III-V SOLAR CELLS The incorporation of nanostructures such as quantum wells or quantum dots into the intrinsic region of p-i-n solar cells has been studied extensively. Recent results show that directional emission from strained quantum wells provides a small but fundamental efficiency enhancement to such devices [1]. An improved understanding of the fundamental processes in these structures may even lead to functional high efficiency cell concepts, such as hot- carrier devices, wherein above-bandgap carriers are collected prior to thermalisation, and intermediate-band devices, where an additional band in the band-gap permits sub-bandgap absorption as a two step process. Preliminary evidence of non-equilibrium carrier populations suggesting delayed cooling is actively being investigated [2,3]. A more immediate benefit to nanostructures comes in the form of subcell bandgap tuning in multijunction solar cells: the inclusion of lower bandgap regions in current-limiting junctions trades extra current for a slight reduction in junction voltage, allowing the other junctions to operate closer to their maximum power point [4], as well as permitting multijunction cells to be tuned to particular insolation spectra. The recent world-record efficiency achieved by a single-junction quantum well solar cell shows that even single-junction nanostructured devices show promise. [5] Nanostructure Example: Quantum Well Solar Cells The production of quantum well solar cells involves growing several interleaved layers of different band-gap lattice-matched materials. There are no binary or ternary alloys with a suitable band-gap that are lattice-matched to GaAs. One candidate, InGaAs, satisfies the band-gap constraints, but its larger lattice constant limits the number of quantum wells; only a few can be grown under compressive strain before relaxation occurs and dislocations form. To counter this problem, it is possible to space the quantum wells not with GaAs, but rather with another material with a smaller lattice constant, such as Figure 1: Quantum Well Solar Cell band structure 978-1-4244-9965-6/11/$26.00 ©2011 IEEE 002615