AVS 62nd International Symposium & Exhibition
    Electronic Materials and Processing Thursday Sessions
       Session EM+EN-ThA

Paper EM+EN-ThA4
Nanowire Enabled 3-Dimensional Band Engineering for Efficient Next Generation Solar Cells

Thursday, October 22, 2015, 3:20 pm, Room 211C

Session: Materials for Light Management
Presenter: Esther Alarcon Llado, Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland
Authors: E. Alarcon Llado, Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland
O. Demichel, Universite de Bourgogne, France
A. Fonctuberta i Morral, Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland
Correspondent: Click to Email
Next generation photovoltaics (PV) aim to achieve large currents at high voltage by new materials and device concepts that overcome the main efficiency losses in traditional solar cells. Intermediate band solar cells (IBSCs) are a class of next generation PV where multi-energy levels in the semiconductor enable the scavenging of low energy photons and converting them into high voltage electrons. IBSCs have only been recently proven with highly mismatched alloys, however with very little efficiencies. The main challenge is the short lifetime of electrons at intermediate band states.

In this regard, the nanowire (NW) geometry offers potential advantages in the solar energy conversion process. Due to their richness in structure and morphology combined with doping and bandgap engineering, NWs provide an opportunity for new charge separation mechanisms.

In this work we propose a new IB-based solar cell design that is advantageously benefited from nanostructuring. We propose the use of core-shell heterostructures in order to reduce the optical coupling between the different band states in a three-level IBSC. Taking advantage of the intrinsic anisotropy of the nanowire geometry, the fundamental idea here is that excitons are separated by the heterostructure along the radial direction, while carrier extraction is performed along the axial direction. As a result, mid-gap recombination rate is reduced by several orders of magnitude.

On the other hand, it is known that optical resonances in NWs result into light self-concentrating effects that allow high absorption with reduced material. What’s more, light resonances in NWs leave a very specific spatial distribution of light inside the nanostructure. By tuning the geometrical parameters of the NW, one can guide light around different regions in the NW depending on the photon energy. A combination of both electrical and morphological engineering, can lead to high efficiency PV.