High-Efficiency Colloidal Quantum Dot Photovoltaics via Robust Self-Assembled Monolayers.

The optoelectronic tunability offered by colloidal quantum dots (CQDs) is attractive for photovoltaic applications but demands proper band alignment at electrodes for efficient charge extraction at minimal cost to voltage. With this goal in mind, self-assembled monolayers (SAMs) can be used to modify interface energy levels locally. However, to be effective SAMs must be made robust to treatment using the various solvents and ligands required for to fabricate high quality CQD solids. We report robust self-assembled monolayers (R-SAMs) that enable us to increase the efficiency of CQD photovoltaics. Only by developing a process for secure anchoring of aromatic SAMs, aided by deposition of the SAMs in a water-free deposition environment, were we able to provide an interface modification that was robust against the ensuing chemical treatments needed in the fabrication of CQD solids. The energy alignment at the rectifying interface was tailored by tuning the R-SAM for optimal alignment relative to the CQD quantum-confined electron energy levels. This resulted in a CQD PV record power conversion efficiency (PCE) of 10.7% with enhanced reproducibility relative to controls.

[1]  Aram Amassian,et al.  Air-stable n-type colloidal quantum dot solids. , 2014, Nature materials.

[2]  Gregory D. Scholes,et al.  Colloidal PbS Nanocrystals with Size‐Tunable Near‐Infrared Emission: Observation of Post‐Synthesis Self‐Narrowing of the Particle Size Distribution , 2003 .

[3]  N. Anderson,et al.  Soluble, Chloride-Terminated CdSe Nanocrystals: Ligand Exchange Monitored by 1H and 31P NMR Spectroscopy , 2013 .

[4]  Udo Bach,et al.  Modification of TiO2 heterojunctions with benzoic acid derivatives in hybrid molecular solid-state devices , 2000 .

[5]  Aram Amassian,et al.  Hybrid passivated colloidal quantum dot solids. , 2012, Nature nanotechnology.

[6]  G. Konstantatos,et al.  Solution-processed PbS quantum dot infrared photodetectors and photovoltaics , 2005, Nature materials.

[7]  Edward H. Sargent,et al.  Materials interface engineering for solution-processed photovoltaics , 2012, Nature.

[8]  Michael D. McGehee,et al.  Effects of molecular interface modification in hybrid organic-inorganic photovoltaic cells , 2007 .

[9]  Edward H. Sargent.  Colloidal quantum dot solar cells , 2012 .

[10]  A. L. da Rosa,et al.  On the stabilization mechanisms of organic functional groups on ZnO surfaces. , 2012, Physical chemistry chemical physics : PCCP.

[11]  William R. Salaneck,et al.  Energy‐Level Alignment at Organic/Metal and Organic/Organic Interfaces , 2009 .

[12]  Illan J. Kramer,et al.  Passivation Using Molecular Halides Increases Quantum Dot Solar Cell Performance , 2016, Advanced materials.

[13]  Sang Il Seok,et al.  High-performance photovoltaic perovskite layers fabricated through intramolecular exchange , 2015, Science.

[14]  Oleksandr Voznyy,et al.  Record Charge Carrier Diffusion Length in Colloidal Quantum Dot Solids via Mutual Dot‐To‐Dot Surface Passivation , 2015, Advanced materials.

[15]  N. H. Moreira,et al.  Functionalization of ZnO surfaces with organic molecules , 2012, OPTO.

[16]  Oleksandr Voznyy,et al.  Infrared Colloidal Quantum Dot Photovoltaics via Coupling Enhancement and Agglomeration Suppression. , 2015, ACS nano.

[17]  Edward H. Sargent,et al.  Inverted Colloidal Quantum Dot Solar Cells , 2014, Advanced materials.

[18]  M. Burgelman,et al.  Advanced electrical simulation of thin film solar cells , 2013 .

[19]  Ratan Debnath,et al.  Depleted-heterojunction colloidal quantum dot solar cells. , 2010, ACS nano.

[20]  Marc Burgelman,et al.  Modeling polycrystalline semiconductor solar cells , 2000 .

[21]  D. Ginger,et al.  Competing Effects of Fluorination on the Orientation of Aromatic and Aliphatic Phosphonic Acid Monolayers on Indium Tin Oxide , 2013 .

[22]  Prashant V. Kamat,et al.  Quantum Dot Solar Cells. Semiconductor Nanocrystals as Light Harvesters , 2008 .

[23]  A Paul Alivisatos,et al.  Air-Stable All-Inorganic Nanocrystal Solar Cells Processed from Solution , 2005, Science.

[24]  A. Heeger,et al.  An Organic Surface Modifier to Produce a High Work Function Transparent Electrode for High Performance Polymer Solar Cells , 2015, Advanced materials.

[25]  Jonathan S. Owen,et al.  Ligand exchange and the stoichiometry of metal chalcogenide nanocrystals: spectroscopic observation of facile metal-carboxylate displacement and binding. , 2013, Journal of the American Chemical Society.

[26]  Moungi G. Bawendi,et al.  Improved performance and stability in quantum dot solar cells through band alignment engineering , 2014, Nature materials.

[27]  Aram Amassian,et al.  Efficient inverted bulk-heterojunction solar cells from low-temperature processing of amorphous ZnO buffer layers , 2014 .

[28]  G. Whitesides,et al.  Self-assembled monolayers of thiolates on metals as a form of nanotechnology. , 2005, Chemical reviews.

[29]  S. Hecht,et al.  Tuning the Work Function of Polar Zinc Oxide Surfaces using Modified Phosphonic Acid Self‐Assembled Monolayers , 2014 .

[30]  N. Tekin,et al.  Polarizabilities and dipole moments of benzaldehyde, benzoic acid and oxalic acid in polar and nonpolar solvents , 2004 .