arXiv subjects

M. J. Burns

Publications and source records attributed to M. J. Burns.

3 recordsLinked to original sources

arXiv2015

The Effects of Geometry on a-Si:H Solar Cell Performance

We present a model for simulating performance of 3D nano -coaxial and -hemispherical thin film solar cells. The material system considered in these simulations is hydrogenated amorphous silicon (a-Si:H), with solar cells fabricated in an n-i-p stacking architecture. Simulations for the performance of the planar a-Si:H device are compared against simulations performed using SCAPS-1D and found to be in close agreement. Electrical and optical properties of devices are discussed for the respective geometries. Maximum power point efficiencies are plotted as a function of i-layer thickness for insight into optimizing spatial parameters. Simulation results show that while geometrical changes in the energy band diagram impact charge carrier collection, a-Si:H solar cell performance is most significantly impacted by light absorption properties associated with nanoscopic arrays of non-planar structures. We compare our simulations to results of fabricated nanocoaxial a-Si:H solar cells and infer the mechanisms of enhanced absorption observed experimentally in such solar cells.

cond-mat.mtrl-sci↗

arXiv2014

Analytical Device-Physics Framework for Non-Planar Solar Cells

Non-planar solar-cell devices have been promoted as a means to enhance current collection in absorber materials with charge-transport limitations. This work presents an analytical framework for assessing the ultimate performance of non-planar solar-cells based on materials and geometry. Herein, the physics of the p-n junction is analyzed for low-injection conditions, when the junction can be considered spatially separable into quasi-neutral and space-charge regions. For the conventional planar solar cell architecture, previously established one-dimensional expressions governing charge carrier transport are recovered from the framework established herein. Space-charge region recombination statistics are compared for planar and non-planar geometries, showing variations in recombination current produced from the space-charge region. In addition, planar and non-planar solar cell performance are simulated, based on a semi-empirical expression for short-circuit current, detailing variations in charge carrier transport and efficiency as a function of geometry, thereby yielding insights into design criteria for solar cell architectures. For the conditions considered here, the expressions for generation rate and total current are shown to universally govern any solar cell geometry, while recombination within the space-charge region is shown to be directly dependent on the geometrical orientation of the p-n junction.

cond-mat.mtrl-sci↗

arXiv2005

Photoinduced time-resolved electrodynamics of superconducting metals and alloys

The photoexcited state in superconducting metals and alloys was studied via pump-probe spectroscopy. A pulsed Ti:sapphire laser was used to create the non-equilibrium state and the far-infrared pulses of a synchrotron storage ring, to which the laser is synchronized, measured the changes in the material optical properties. Both the time- and frequency- dependent photoinduced spectra of Pb, Nb, NbN, Nb{0.5}Ti{0.5}N, and Pb{0.75}Bi{0.25} superconducting thin films were measured in the low-fluence regime. The time dependent data establish the regions where the relaxation rate is dominated either by the phonon escape time (phonon bottleneck effect) or by the intrinsic quasiparticle recombination time. The photoinduced spectra measure directly the reduction of the superconducting gap due to an excess number of quasiparticles created by the short laser pulses. This gap shift allows us to establish the temperature range over which the low fluence approximation is valid.

cond-mat.supr-con↗