GaAs p-i-n solar cells embedded with varying number of QD layers (0-60) were grown by OMVPE. 1x1 cm2 cells were fabricated and standard solar cell testing was performed. Illuminated AM0 current-voltage characteristics
were measured of both a baseline and 10-layer quantum dot (QD) embedded GaAs p-i-n. The QD solar cell (QDSC)
gave an short circuit current of 23.1 mA/cm2 increase in of 0.7mA/cm2 above the baseline with no QDs. The QD
embedded cell also showed limited loss in open circuit voltage characteristics of 0.99 V compared to 1.04 V of the
baseline. Conversion efficiencies were 13.4 and 13.8 for the QDSC and baseline solar cell, respectively. Spectral
responsivity measurements revealed equivalent GaAs response in the visible for the baseline, 10x and 20x layer QD
samples, while systematically degraded emitter lifetime was found to be responsible for loss in visible responsivities for
the 60x QDSC. Sub-GaAs bandgap response gave a systematic increase of 0.25 mA/QD layer. Spectral responsivity
modeling was used and found that bulk GaAs emitter and i-region lifetimes degraded from 102 ns to 102 ps, with
increasing number of QD layers.
State of the art photovoltaics exhibiting conversion efficiency in excess of 30% (1-sun) utilize epitaxially grown
multijunction III-V materials. Increasing photovoltaic efficiency is critically important to the space power, and more
recently, the terrestrial concentrator PV communities
The use of nanostructured materials within photovoltaic devices can enable improved efficiency, potentially in excess of
the Shockley-Queisser limit. The addition of nanostructures such as quantum dots (QDs) to photovoltaic devices allows
one to extend the absorption spectrum of the solar cell and "tune" the bandgap to the spectral conditions. Multi-junction
(MJ) solar cells would benefit from the additional short-circuit current within the middle current-limiting (In)GaAs cell
via QD spectral tuning. While QD tuning is a potentially direct approach to increased efficiency of MJ solar cells, it has
been reported that significant improvements can be achieved using QDs to form an intermediate band within the
bandgap of a suitable matrix.
We will discuss the potential for QD photovoltaic devices and examine the challenges associated with multi-junction
device growth with the inclusion of quantum dot arrays. GaAs p-i-n solar cells, with and without InAs QD superlattices
are used to demonstrate the potential benefits of QDs. The unique challenges associated with the characterization of this
type of device will also be presented. Using strain-balanced Stranski-Krastanov QD formation, we have demonstrated
sub-gap photon collection and increased current in QD-enhanced GaAs solar cells containing up to 100 periods. Finally,
we will discuss the opportunities that these devices hold for high photovoltaic conversion efficiency.
Quantum dot enhanced solar cells have been evaluated both theoretically and experimentally. A detailed balance simulation of InAs quantum dot (QD) enhanced solar cells has been performed. A 14% (absolute) efficiency improvement has been predicted if the middle junction of a state-of-the-art space multi-junction III-V solar cell can be bandgap engineered using QDs. Experimental results for a GaAs middle junction enhanced with InAs QDs have shown an 8% increase in short circuit current compared to a baseline device. The current enhancement per layer of QD was extracted from device spectral response (0.017 mA per QD layer). This value was used to estimate the efficiency of multi-junction solar cells with up to 200 layers of QDs added to the middle current-limiting junction. In addition, the radiation tolerance of QD cells, key to operation of these cells in space environments, shows improved characteristics. Open circuit voltage (VOC) in QD devices was more resilient to both alpha and proton displacement damage, resulting in a 10X reduction in the rate of VOC degradation.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.