Measuring and Controlling the Electronic Structure of PbS QDs

Matthew Beard^a, Craig Perkins^a, Jianbing Zhang^a, Jao van de Lagemaat^a, Joseph Luther^a, Elisa Miller^a, Daniel Kroupa^a, Ryan Crisp^a, Antoine Kahn^b, Philip Schulz^b

^aNREL, 16253 Denver West Parkway, Golden, 80401, United States

^bDepartment of Electrical Engineering, Princeton University, Department of Electrical Engineering, Princeton University, Princeton, NJ 08544, United States

^cChemical and Biosciences Department, University of Colorado, Boulder, University of Colorado, Chemical and Biosciences Department, Boulder, Colorado 80309, United States

^dDepartment of Physics, Colorado School of Mines, Department of Physics, Colorado School of Mines, Golden, CO 80401, United States

Materials for Sustainable Development Conference (MATSUS)
Proceedings of nanoGe September Meeting 2015 (NFM15)

Santiago de Compostela, Spain, 2015 September 6th - 15th

Oral, Elisa Miller, presentation 046
Publication date: 8th June 2015

Quantum Dot (QD) solar cells are an active area of photovoltaics (PVs) research due to their potential to be competitive devices in the PV market. Tuning the band alignment of PbS QD solar cells enhances solar cell efficiencies; therefore, it is important to correctly quantify the valence band maximum (VBM) and conduction band minimum (CBM). The PV community typically relies on X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) measurements for the QD band energies. These XPS/UPS measurements are used to directly measure the VBM and indirectly determine the CBM. For size-selected PbS QDs, previous photoelectron spectroscopy reports have determined that the VBM is independent of the PbS QD size and, therefore, only the CBM is dependent on the QD size. We show with a comprehensive XPS/UPS study on size-selected PbS QDs that the previous results are incorrectly interpreted and that both the VBM and CBM energies are dependent on the PbS QD size. This is shown through a combination of UPS/XPS, inverse photoelectron spectroscopy (IPES) measurements, effective mass approximation, GW calculations, and other experimental techniques. With this knowledge, we show that XPS VB measurements can still be used to study the effects of surface treatments. We show that the Fermi level to VB position can be controlled with different surface treatments, such as TBAI, MPA, PbI₂, and Na₂S, to make the PbS QD thin films more n- or p-type; however, we do not assign absolute energies to the VBM or CBM through these measurements.

nanoGe is a prestigious brand of successful science conferences that are developed along the year in different areas of the world since 2009. Our worldwide conferences cover cutting-edge materials topics like perovskite solar cells, photovoltaics, optoelectronics, solar fuel conversion, surface science, catalysis and two-dimensional materials, among many others.

MATSUS

Previously nanoGe Spring Meeting (NSM) and nanoGe Fall Meeting (NFM), MATSUS is a multiple symposia conference focused on a broad set of topics of advanced materials preparation, their fundamental properties, and their applications, in fields such as renewable energy, photovoltaics, lighting, semiconductor quantum dots, 2-D materials synthesis, charge carriers dynamics, microscopy and spectroscopy semiconductors fundamentals, etc.

International Conference on Hybrid and Organic Photovoltaics

International Conference on Hybrid and Organic Photovoltaics (HOPV) is celebrated yearly in May. The main topics are the development, function and modeling of materials and devices for hybrid and organic solar cells. The field is now dominated by perovskite solar cells but also other hybrid technologies, as organic solar cells, quantum dot solar cells, and dye-sensitized solar cells and their integration into devices for photoelectrochemical solar fuel production.

Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics

The main topics of the Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics (IPEROP) are discussed every year in Asia-Pacific for gathering the recent advances in the fields of material preparation, modeling and fabrication of perovskite and hybrid and organic materials. Photovoltaic devices are analyzed from fundamental physics and materials properties to a broad set of applications. The conference also covers the developments of perovskite optoelectronics, including light-emitting diodes, lasers, optical devices, nanophotonics, nonlinear optical properties, colloidal nanostructures, photophysics and light-matter coupling.

International Conference on Perovskite Thin Film Photovoltaics Perovskite Photonics and Optoelectronics

The International Conference on Perovskite Thin Film Photovoltaics Perovskite Photonics and Optoelectronics (NIPHO) is the best place to hear the latest developments in perovskite solar cells as well as on recent advances in the fields of perovskite light-emitting diodes, lasers, optical devices, nanophotonics, nonlinear optical properties, colloidal nanostructures, photophysics and light-matter coupling.