1. Energy of the Future: Solar Cells Rade Kuljic 1, Hyeson Jung 1, Ayan Kar 1, Michael A. Stroscio 1,2 and Mitra Dutta 1,3 1 Department of Electrical and Computer Engineering, University of Illinois at Chicago 2 Department of Bioengineering, University of Illinois at Chicago, 3 Department of Physics, University of Illinois at Chicago Problem Statement and Motivation CdTe Thin Film Solar Cell PbSe Nanowires for Photovoltaic Applications  Motivation  Quantum confinement in nanowires should improve the charge transport in solar cells.  Promising materials for tandem solar cells for higher conversion efficiency.  Key achievement  PbSe nanowires were grown by magnetron sputtering.  Closed packed PbSe nanowires of 100 nm grown.  The surface of nanowires was strongly oxidized during post annealing process.  These large diameter wires showed a surprising large blue shift demonstrating quantum confinement.  Attributed to Fermi level pinning, strong band bending and a wide depletion layer.  Effective confinement diameter is around 10 nm. SEM images: Surface view (top) and cross-sectional side view (bottom) of grown nanowires. Schematic illustration of the Fermi-level pinning at the nanowire surface due to surface oxidization. N NanoEngineering Research Laboratory (111)  110  (a) FTIR spectrum and (b) PL spectrum of the PbSe nanowires are presented. Cut-off wavelength at 2.5  m and PL peak at 2.45  m are found, despite energy band gap of bulk PbSe crystal is 4.46  m at 300K.  Motivation  First generation solar cell - efficient but relatively expensive.  Current commercial solar cells - single/poly crystalline silicon.  Recently, silicon wafers price increased substantially (3X).  Second generation solar cells - amorphous Si, CdTe, and CIGS thin film cells can be competitive due to an optimal trade-off between manufacturing cost and conversion efficiency.  CdTe solar cells have higher efficiency than a-Si cells.  Direct energy bandgap of CdTe is 1.5 eV, considered as optimal for maximum photovoltaic conversion, results in high optical absorption.  Thin-film CdTe provide a cost effective solar cell design.  Key achievement and future goals  In this study, CdTe solar cells were fabricated and tested; the thin films were grown by e-beam evaporation and magnetron sputtering, followed by annealing.  12 % efficiency achieved with first efforts.  Incorporating nanostructures we hope to achieve higher efficiency via such mechanisms as the Resonant Energy Transfer (RET), Multiple Exciton Generation (MEG) and light scattering. Cross-section view p-type CdTe ~4.5 μm n-type CdS ~ 0.2 μm Front contact SnO2:F ~ 0.2 μm glass Solar spectral irradiance (red) and ideal conversion efficiency of most common inorganic solar cells (green) Butterfly toys powered up with our CdTe cells I-V characteristic of our record cell with efficiency of 12.16% SEM cross sectional view of the fabricated CdTe cells  Energy deficit is one of the most challenging issues facing near future.  Crude oil resources are rapidly declining due to recently increased energy demand.  Fossil fuels are accompanied with greenhouse emissions that negatively affect the natural environment, climate change, and public health.  Nuclear energy is usually associated with public safety and health concerns.  Hydro, wind and geothermal power are dependent on various geographical conditions, thus not capable to provide a sustainable energy source.  Solar technology, providing a renewable, widely spread, environmentally friendly and inexpensive source of energy, offers the best solution to overcome energy deficit in the future.