skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Theory of photovoltaic characteristics of semiconductor quantum dot solar cells

Abstract

We develop a comprehensive rate equations model for semiconductor quantum dot solar cells (QDSCs). The model is based on the continuity equations with a proper account for quantum dots (QDs). A general analytical expression for the total current density is obtained, and the current-voltage characteristic is studied for several specific situations. The degradation in the open circuit voltage of the QDSC is shown to be due to strong spontaneous radiative recombination in QDs. Due to small absorption coefficient of the QD ensemble, the improvement in the short circuit current density is negligible if only one QD layer is used. If spontaneous radiative recombination would be suppressed in QDs, a QDSC with multiple QD layers would have significantly higher short circuit current density and power conversion efficiency than its conventional counterpart. The effects of photoexcitation of carriers from discrete-energy states in QDs to continuum-energy states are discussed. An extended model, which includes excited states in QDs, is also introduced.

Authors:
 [1];  [2];  [3]
  1. Low Carbon Energy Institute, China University of Mining and Technology, Xuzhou 221116 (China)
  2. (China)
  3. Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 (United States)
Publication Date:
OSTI Identifier:
22598877
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 120; Journal Issue: 8; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ABSORPTION; CONTINUITY EQUATIONS; CURRENT DENSITY; ELECTRIC POTENTIAL; ELECTRICAL FAULTS; EXCITED STATES; LAYERS; PHOTOVOLTAIC EFFECT; QUANTUM DOTS; REACTION KINETICS; RECOMBINATION; SEMICONDUCTOR MATERIALS; SOLAR CELLS

Citation Formats

Wu, Yuchang, E-mail: yuchangw@cumt.edu.cn, School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou 221116, and Asryan, Levon V., E-mail: asryan@vt.edu. Theory of photovoltaic characteristics of semiconductor quantum dot solar cells. United States: N. p., 2016. Web. doi:10.1063/1.4961046.
Wu, Yuchang, E-mail: yuchangw@cumt.edu.cn, School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou 221116, & Asryan, Levon V., E-mail: asryan@vt.edu. Theory of photovoltaic characteristics of semiconductor quantum dot solar cells. United States. doi:10.1063/1.4961046.
Wu, Yuchang, E-mail: yuchangw@cumt.edu.cn, School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou 221116, and Asryan, Levon V., E-mail: asryan@vt.edu. Sun . "Theory of photovoltaic characteristics of semiconductor quantum dot solar cells". United States. doi:10.1063/1.4961046.
@article{osti_22598877,
title = {Theory of photovoltaic characteristics of semiconductor quantum dot solar cells},
author = {Wu, Yuchang, E-mail: yuchangw@cumt.edu.cn and School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou 221116 and Asryan, Levon V., E-mail: asryan@vt.edu},
abstractNote = {We develop a comprehensive rate equations model for semiconductor quantum dot solar cells (QDSCs). The model is based on the continuity equations with a proper account for quantum dots (QDs). A general analytical expression for the total current density is obtained, and the current-voltage characteristic is studied for several specific situations. The degradation in the open circuit voltage of the QDSC is shown to be due to strong spontaneous radiative recombination in QDs. Due to small absorption coefficient of the QD ensemble, the improvement in the short circuit current density is negligible if only one QD layer is used. If spontaneous radiative recombination would be suppressed in QDs, a QDSC with multiple QD layers would have significantly higher short circuit current density and power conversion efficiency than its conventional counterpart. The effects of photoexcitation of carriers from discrete-energy states in QDs to continuum-energy states are discussed. An extended model, which includes excited states in QDs, is also introduced.},
doi = {10.1063/1.4961046},
journal = {Journal of Applied Physics},
number = 8,
volume = 120,
place = {United States},
year = {Sun Aug 28 00:00:00 EDT 2016},
month = {Sun Aug 28 00:00:00 EDT 2016}
}
  • Here, we will first briefly summarize the general principles of QD synthesis using our previous work on InP as an example. Then we will focus on QDs of the IV-VI Pb chalcogenides (PbSe, PbS, and PbTe) and Si QDs because these were among the first QDs that were reported to produce multiple excitons upon absorbing single photons of appropriate energy (a process we call multiple exciton generation (MEG)). We note that in addition to Si and the Pb-VI QDs, two other semiconductor systems (III-V InP QDs(56) and II-VI core-shell CdTe/CdSe QDs(57)) were very recently reported to also produce MEG. Thenmore » we will discuss photogenerated carrier dynamics in QDs, including the issues and controversies related to the cooling of hot carriers and the magnitude and significance of MEG in QDs. Finally, we will discuss applications of QDs and QD arrays in novel quantum dot PV cells, where multiple exciton generation from single photons could yield significantly higher PV conversion efficiencies.« less
  • Quantum dot-sensitized solar cells (QDSSCs) have emerged as a promising solar architecture for next-generation solar cells. The QDSSCs exhibit a remarkably fast electron transfer from the quantum dot (QD) donor to the TiO 2 acceptor with size quantization properties of QDs that allows for the modulation of band energies to control photoresponse and photoconversion efficiency of solar cells. In order to understand the mechanisms that underpin this rapid charge transfer, the electronic properties of CdSe and PbSe QDs with different sizes on the TiO 2 substrate are simulated using a rigorous ab initio density functional method. Our method capitalizes onmore » localized orbital basis set, which is computationally less intensive. Quite intriguingly, a remarkable set of electron bridging states between QDs and TiO 2 occurring via the strong bonding between the conduction bands of QDs and TiO 2 is revealed. Such bridging states account for the fast adiabatic charge transfer from the QD donor to the TiO 2 acceptor, and may be a general feature for strongly coupled donor/acceptor systems. All the QDs/TiO 2 systems exhibit type II band alignments, with conduction band offsets that increase with the decrease in QD size. This facilitates the charge transfer from QDs donors to TiO 2 acceptors and explains the dependence of the increased charge transfer rate with the decreased QD size.« less
  • The current-voltage (J-V) characteristics of ZnO/PbS quantum dot (QD) solar cells show a QD size-dependent behavior resulting from a Schottky junction that forms at the back metal electrode opposing the desirable diode formed between the ZnO and PbS QD layers. We study a QD size-dependent roll-over effect that refers to the saturation of photocurrent in forward bias and crossover effect which occurs when the light and dark J-V curves intersect. We model the J-V characteristics with a main diode formed between the n-type ZnO nanocrystal (NC) layer and p-type PbS QD layer in series with a leaky Schottky-diode formed betweenmore » PbS QD layer and metal contact. We show how the characteristics of the two diodes depend on QD size, metal work function, and PbS QD layer thickness, and we discuss how the presence of the back diode complicates finding an optimal layer thickness. Finally, we present Kelvin probe measurements to determine the Fermi level of the QD layers and discuss band alignment, Fermi-level pinning, and the V oc within these devices.« less