Engineering topics

VanOrman, Zachary A.

Publications and source records attributed to VanOrman, Zachary A..

6 records

DOE OSTI2022

Surface Doping Boosts Triplet Generation Yield in Perovskite-Sensitized Upconversion

Triplet–triplet annihilation-based photon upconversion (TTA-UC) can efficiently generate higher energy photons at low relative fluences. Bulk metal halide perovskites have offered promise in efficiently sensitizing molecular triplet states in the solid state, necessary for the integration of TTA-UC into device-based applications. Recent work focused on TTA-UC from a rubrene triplet annihilator sensitized by perovskite thin films has established relatively efficient charge extraction from the perovskite, forming the triplet exciton in rubrene. Yet, the specifics underpinning charge transfer at the perovskite/rubrene interface are not fully elucidated. Here, to improve device performance and study the properties governing charge transfer at the interface, various organic solvents are explored to treat the perovskite surface. Scanning tunneling microscopy and spectroscopy show a difference in the electronic band structure, where both n- and p-type terminated perovskite surfaces are observed depending on the solvent used. Supported by optical spectroscopy, the impact of the perovskite electronic structure is monitored, indicating that n-type perovskite sensitizers feature higher TTA-UC efficiencies due to favorable band bending resulting in efficient hole-mediated triplet formation. Overall, the tuning of the electronic structure of the perovskite sensitizer through solvent treatment is shown to be a key force in tuning the mechanism of efficient triplet generation.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Ultrafast Triplet Generation at the Lead Halide Perovskite/Rubrene Interface

Triplet sensitization of rubrene by bulk lead halide perovskites has recently resulted in efficient infrared-to-visible photon upconversion via triplet-triplet annihilation. Notably, this process can occur under solar relevant fluxes, potentially paving the way toward integration with photovoltaic devices. In order to further improve the upconversion efficiency, the fundamental photophysical pathways at the perovskite/rubrene interface must be clearly understood to maximize charge extraction. Here, we utilize ultrafast transient absorption spectroscopy to elucidate the processes underlying triplet generation at the perovskite/rubrene interface. In this work, our results point to a triplet generation mechanism based on hot carriers; thermally excited charge carriers in the perovskite cool more rapidly in the presence of rubrene, suggesting rapid extraction of these thermally excited carriers on the picosecond time scale. Subsequent triplet formation in rubrene is observed on a subnanosecond time scale.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Mixed halide bulk perovskite triplet sensitizers: Interplay between band alignment, mid-gap traps, and phonons

Photon upconversion, particularly via triplet-triplet annihilation (TTA), could prove beneficial in expanding the efficiencies and overall impacts of optoelectronic devices across a multitude of technologies. The recent development of bulk metal halide perovskites as triplet sensitizers is one potential step toward the industrialization of upconversion-enabled devices. In this work, we investigate the impact of varying additions of bromide into a lead iodide perovskite thin film on the TTA upconversion process in the annihilator molecule rubrene. We find an interplay between the bromide content and the overall device efficiency. In particular, a higher bromide content results in higher internal upconversion efficiencies, enabled by more efficient charge extraction at the interface, likely due to a more favorable band alignment. However, the external upconversion efficiency decreases, as the absorption cross section in the near infrared is reduced. The highest upconversion performance is found in our study for a bromide content of 5%. This result can be traced back to a high absorption cross section in the near infrared and higher photoluminescence quantum yield in comparison to the iodide-only perovskite, as well as an increased driving force for charge transfer.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Impact of Transition Metal Doping on the Structural and Optical Properties of Halide Perovskites

Metal ion doping into halide perovskite materials is a promising approach to enhance long-term film stability and improve solar cell performance. Moreover, the idea of doping metals into halide perovskites is also driven by applications in heterogeneous catalysis. Here, we investigate the incorporation of the transition metals Pt and Pd into mixed-halide perovskite materials. We find that Pt aggregates in large clusters in iodine- and bromine-rich perovskite film compositions, whereas Pd incorporation depends on the underlying bromine to iodine ratio. Furthermore, by using optical and structural characterization methods, we observe that phase segregation in the perovskite layer is suppressed upon doping of either of these metals into the material. This approach further shows the potential to obtain catalytically active halide perovskite films in which the perovskite can serve as a host matrix.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Bulk halide perovskites as triplet sensitizers: progress and prospects in photon upconversion

Triplet–triplet annihilation-based photon upconversion (TTA-UC) is a promising mechanism for harvesting lower energy photons by converting them to a higher energy. Photons generated from this process can be used for numerous applications, including photovoltaics, infrared sensing and imaging, biomedicine and photochemical reactions. Recently, bulk metal halide perovskite semiconductors have been introduced as triplet sensitizers for the TTA-UC process. While relatively efficient upconversion has been achieved at low fluences, the full potential of these materials as triplet sensitizers has not been unlocked. In this study, we examine four pathways for device optimization and improvements, while discussing relevant works and potential further improvements. Finally, we discuss the outlook and bright future of such perovskite materials as triplet sensitizers and their important role in solid-state upconversion applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2020

Halide Perovskites: A Progress Report on Photon Interconversion

Photon interconversion generally describes processes which change the wavelength of the emitted light upon irradiation, with a gain in photon energy (upconversion), or a splitting of the incident photon energy to create multiple photons (downconversion). The focus of this progress report is placed on halide perovskite materials and their role in upconversion by triplet-triplet annihilation and downconversion via singlet fission in organic semiconductors, and a short perspective is given into quantum cutting and lanthanide-based upconversion applications. The current advances are highlighted regarding halide perovskites and perovskite-inspired materials with varying framework and material dimensionalities, as relating to photon interconversion processes. Here, the majority of the literature is based on 3D perovskites, which leaves room for growth for perovskite materials with varying dimensionalities. Gaps in the current field are emphasized, leading to a bright outlook on future possibilities of coupling perovskites to photon interconversion mechanisms, which can open the door for future breakthroughs in this field.

36 MATERIALS SCIENCE↗