Optoelectronic Devices
Magnetic field-switchable laser via optical pumping of rubrene.
Collin F. Perkinson et al. Advanced Materials 2021, 2103870.
Volumetric optical imaging of magnetic fields is challenging with existing magneto-optical materials, motivating the search for dyes with strong magnetic field interactions, distinct emission spectra, and an ability to withstand high photon flux and incorporation within samples. Here, the magnetic field effect on singlet-exciton fission is exploited to demonstrate spatial imaging of magnetic fields in a thin film of rubrene. This is thought to be the first demonstration of a magnetically switchable laser, as well as the largest magnetically induced change in emission brightness in a singlet-fission material to date. These results demonstrate that singlet-fission materials are promising materials for magnetic sensing applications and could inspire a new class of magneto-optical modulators.
Triplet-Sensitization by Lead Halide Perovskite Thin Films for Near-Infrared-to-Visible Upconversion.
Lea Nienhaus et al. ACS Energy Letters 2019, 4 (4), 888-895.
Lead halide-based perovskite thin films have attracted great attention due to the rapid increase in perovskite solar cell efficiencies. The same optoelectronic properties that make perovskites ideal absorber materials in solar cells are also beneficial in other light-harvesting applications and make them prime candidates as triplet sensitizers in upconversion via triplet–triplet annihilation in rubrene. In this contribution, we take advantage of long carrier lifetimes and carrier diffusion lengths in perovskite thin films, their high absorption cross-sections throughout the visible spectrum, and the strong spin–orbit coupling owing to the abundance of heavy atoms to sensitize the upconverter rubrene. Our bilayer device exhibits an upconversion efficiency in excess of 3% under 785 nm illumination at an incident power of ∼88 W/cm2.
An interface stabilized perovskite solar cell with high stabilized efficiency and low voltage loss.
Jason J. Yoo et al. Energy & Environmental Science 2019, 12, 2192.
Stabilization of the crystal phase of inorganic/organic lead halide perovskites is critical for their high performance optoelectronic devices. While various surface passivating agents have been developed to improve the device performance of perovskite solar cells, conventional deposition methods using a protic polar solvent, mainly isopropyl alcohol (IPA), results in a destabilization of the underlying perovskite layer and an undesirable degradation of device properties. We demonstrate the hidden role of IPA in surface treatments and develop a strategy in which the passivating agent is deposited without destabilizing the high quality perovskite underlayer. This strategy results in an open-circuit-voltage loss of only ∼340 mV, a champion device with a power conversion efficiency of 23.4% from a reverse current–voltage scan, a device with a record certified stabilized PCE of 22.6%, and enhanced operational stability.
Lili Wang et al. Advanced materials 2021, 33, 2100854.
Photon upconversion via triplet-triplet annihilation (TTA) has promise for overcoming the Shockley-Queisser limit for single-junction solar cells by allowing the utilization of sub-bandgap photons. Recently, bulk perovskites have been employed as sensitizers in solid-state upconversion devices to circumvent poor exciton diffusion in previous nanocrystal (NC)-sensitized devices. However, an in-depth understanding of the underlying photophysics of perovskite-sensitized triplet generation is still lacking due to the difficulty of precisely controlling interfacial properties of fully solution-processed devices. In this study, interfacial properties of upconversion devices are adjusted by a mild surface solvent treatment, specifically altering perovskite surface properties without perturbing the bulk perovskite.
Collin F. Perkinson et al. J. Chem. Phys. 2019, 151, 121102.
Singlet exciton fission is a mechanism that could potentially enable solar cells to surpass the Shockley-Queisser efficiency limit by converting single high-energy photons into two lower-energy triplet excitons with minimal thermalization loss. The ability to make use of singlet exciton fission to enhance solar cell efficiencies has been limited, however, by the sparsity of singlet fission materials with triplet energies above the bandgaps of common semiconductors such as Si and GaAs. Here, we employ a high-throughput virtual screening procedure to discover new organic singlet exciton fission candidate materials with high-energy (>1.4 eV) triplet excitons.
Lea Nienhaus et al. ACS Nano 2017, 11, 7848-7857.
Hybrid interfaces combining inorganic and organic materials underpin the operation of many optoelectronic and photocatalytic systems and allow for innovative approaches to photon up- and down-conversion. However, the mechanism of exchange-mediated energy transfer of spin-triplet excitons across these interfaces remains obscure, particularly when both the macroscopic donor and acceptor are composed of many separately interacting nanoscopic moieties. Here, we study the transfer of excitons from colloidal lead sulfide (PbS) nanocrystals to the spin-triplet state of rubrene molecules. Using nanocrystals with these optimal-length ligands in an improved solid-state device structure, we obtain an upconversion efficiency of (7 ± 1)% with excitation at λ = 808 nm.
Efficient perovskite solar cells via improved carrier management .
Jason J. Yoo et al. Nature 2021, 590, 587593.
We report a holistic approach to improving the performance of metal halide perovskite solar cells (PSCs) through enhanced charge carrier management. First, we develop an electron transport layer with an ideal film coverage, thickness and composition by tuning the chemical bath deposition of tin dioxide (SnO2). Second, we decouple the passivation strategy between the bulk and the interface, leading to improved properties, while minimizing the bandgap penalty. In forward bias, our devices exhibit an electroluminescence external quantum efficiency of up to 17.2 per cent and an electroluminescence energy conversion efficiency of up to 21.6 per cent. As solar cells, they achieve a certified power conversion efficiency of 25.2 per cent, corresponding to 80.5 per cent of the thermodynamic limit of its bandgap.
Decreased Synthesis Costs and Waste Product Toxicity for Lead Sulfide Quantum Dot Ink Photovoltaics.
Nicole Moody et al. Advanced Sustainable Systems 2019.
Use of lead sulfide (PbS) colloidal quantum dot (QD) films as photoactive layers in photovoltaic (PV) devices typically requires replacement of native QD ligands with lead‐based capping ligands (i.e., PbX2, X = Br, I) for the best‐performing QD PVs. This ligand replacement process often requires additional solvents and toxic reagents. In the present study, an alternative PbS QD PV fabrication method with a lead‐free tetrabutylammonium iodide (TBAI) ligand source and lower material requirements and toxicity is demonstrated, yielding 10% power conversion efficient PVs with more than 1000 h of storage stability under ambient conditions.