Halide perovskite solar cells have seen dramatic progress in performance over the past several years. Certified efficiencies of inverted structure (p-i-n) devices have now exceeded 20%. In these ...p-i-n devices, fullerene compounds are the most popular electron-transfer materials. However, the full function of fullerenes in perovskite solar cells is still under investigation, and the mechanism of photocurrent hysteresis suppression by fullerene remains unclear. In previous reports, thick fullerene layers (>20 nm) were necessary to fully cover the perovskite film surface to make good contact with perovskite film and avoid large leakage currents. In addition, the solution-processed fullerene layer has been broadly thought to infiltrate into the perovskite film to passivate traps on grain boundary surfaces, causing suppressed photocurrent hysteresis. In this work, we demonstrate an efficient perovskite photovoltaic device with only 1 nm C60 deposited by vapor deposition as the electron-selective material. Utilizing a combination of fluorescence microscopy and impedance spectroscopy, we show that the ultrathin C60 predominately acts to extract electrons from the perovskite film while concomitantly suppressing the photocurrent hysteresis by reducing space charge accumulation at the interface. This work ultimately helps to clarify the dominant role of fullerenes in perovskite solar cells while simplifying perovskite solar cell design to reduce manufacturing costs.
Transparent luminescent solar concentrators are a new standard for selective light harvesting allowing for non‐tinted, transparent, and highly scalable solar windows. These devices are enabled by ...exploiting phosphorescent hexanuclear nanocrystalline‐polymer blends that exhibit massive Stokes‐shifts, high phosphorescent quantum yield, high stability, and perfectly tuned absorption/emission around the visible spectrum.
The electronic properties of colloidal quantum dots (QDs) are critically dependent on both QD size and surface chemistry. Modification of quantum confinement provides control of the QD bandgap, while ...ligand-induced surface dipoles present a hitherto underutilized means of control over the absolute energy levels of QDs within electronic devices. Here, we show that the energy levels of lead sulfide QDs, measured by ultraviolet photoelectron spectroscopy, shift by up to 0.9 eV between different chemical ligand treatments. The directions of these energy shifts match the results of atomistic density functional theory simulations and scale with the ligand dipole moment. Trends in the performance of photovoltaic devices employing ligand-modified QD films are consistent with the measured energy level shifts. These results identify surface-chemistry-mediated energy level shifts as a means of predictably controlling the electronic properties of colloidal QD films and as a versatile adjustable parameter in the performance optimization of QD optoelectronic devices.
Photoactive agents are promising complements for both early diagnosis and targeted treatment of cancer. The dual combination of diagnostics and therapeutics is known as theranostics. Photoactive ...theranostic agents are activated by a specific wavelength of light and emit another wavelength, which can be detected for imaging tumors, used to generate reactive oxygen species for ablating tumors, or both. Photodynamic therapy (PDT) combines photosensitizer (PS) accumulation and site-directed light irradiation for simultaneous imaging diagnostics and spatially targeted therapy. Although utilized since the early 1900s, advances in the fields of cancer biology, materials science, and nanomedicine have expanded photoactive agents to modern medical treatments. In this review we summarize the origins of PDT and the subsequent generations of PSs and analyze seminal research contributions that have provided insight into rational PS design, such as photophysics, modes of cell death, tumor-targeting mechanisms, and light dosing regimens. We highlight optimizable parameters that, with further exploration, can expand clinical applications of photoactive agents to revolutionize cancer diagnostics and treatment.
Visibly transparent solar harvesting surfaces are an exciting new approach to harvesting solar energy around buildings and mobile electronics to improve their efficiency and autonomy without ...impacting their appearance. The recent demonstration of ultraviolet (UV) and near‐infrared (NIR) selective light harvesters have enabled transparent luminescent solar concentrators (LSCs) that boast unparalleled scalability, flexibility, aesthetic quality, and affordability. Consequently, the question of the efficiency limits has emerged in these new systems. In this perspective, the theoretical efficiency limits of these concentrator systems are reviewed and practical considerations are outlined to approach these limits. For UV and UV/NIR selective harvesting single‐junction transparent LSCs are constrained thermodynamically to 21%, which increases to over 35% in fully transparent multipanel devices with light trapping. In deriving these limits, key material and engineering challenges are identified to fully optimize transparent solar concentrators that can push them towards commercial reality.
Transparent luminescent solar concentrators provide new routes to deploy solar energy over large areas without affecting the overall aesthetic quality. These new solar technologies are enabled by selectively harvesting ultraviolet or infrared parts of the solar spectrum. In this report, these systems are reviewed in the context of idealized configurations, efficiency limits, scalability, and properties of enabling classes of materials.
Halide perovskite solar cells have seen dramatic progress in performance over the past several years. Certified efficiencies of inverted structure (p-i-n) devices have now exceeded 20%. In these ...p-i-n devices, fullerene compounds are the most popular electron-transfer materials. However, the full function of fullerenes in perovskite solar cells is still under investigation, and the mechanism of photocurrent hysteresis suppression by fullerene remains unclear. In previous reports, thick fullerene layers (>20 nm) were necessary to fully cover the perovskite film surface to make good contact with perovskite film and avoid large leakage currents. In addition, the solution-processed fullerene layer has been broadly thought to infiltrate into the perovskite film to passivate traps on grain boundary surfaces, causing suppressed photocurrent hysteresis. In this work, we demonstrate an efficient perovskite photovoltaic device with only 1 nm C
deposited by vapor deposition as the electron-selective material. Utilizing a combination of fluorescence microscopy and impedance spectroscopy, we show that the ultrathin C
predominately acts to extract electrons from the perovskite film while concomitantly suppressing the photocurrent hysteresis by reducing space charge accumulation at the interface. This work ultimately helps to clarify the dominant role of fullerenes in perovskite solar cells while simplifying perovskite solar cell design to reduce manufacturing costs.
The effect of crystalline order on the exciton diffusion length (LD) is shown for the archetypal organic semiconductor 3,4,9,10‐perylenetetracarboxylic dianhydride (PTCDA; see figure). LD increases ...from ∼6.5 nm in the amorphous limit to ∼25 nm for single crystals. These changes in diffusion length are connected to changes in the fluorescence quantum yield, which is useful for understanding where crystal‐size‐dependant diffusion trends are likely to be observed for other organic materials.
Photodynamic therapy (PDT) has the potential to improve cancer treatment by providing dual selectivity through the use of both photoactive agent and light, with the goal of minimal harmful effects ...from either the agent or light alone. However, current PDT is limited by insufficient photosensitizers (PSs) that can suffer from low tissue penetration, insufficient phototoxicity (toxicity with light irradiation), or undesirable cytotoxicity (toxicity without light irradiation). Recently, we reported a platform for decoupling optical and electronic properties with counterions that modulate frontier molecular orbital levels of a photoactive ion. Here, we demonstrate the utility of this platform in vivo by pairing near-infrared (NIR) photoactive heptamethine cyanine cation (Cy+), which has enhanced optical properties for deep tissue penetration, with counterions that make it cytotoxic, phototoxic, or nontoxic in a mouse model of breast cancer. We find that pairing Cy+ with weakly coordinating anion FPhB– results in a selectively phototoxic PS (CyFPhB) that stops tumor growth in vivo with minimal side effects. This work provides proof of concept that our counterion pairing platform can be used to generate improved cancer PSs that are selectively phototoxic to tumors and nontoxic to normal healthy tissues.
We demonstrate single-walled carbon nanotube (SWCNT)/P3HT polymer bulk heterojunction solar cells with an AM1.5 efficiency of 0.72%, significantly higher than previously reported (0.05%). A key step ...in achieving high efficiency is the utilization of semiconducting SWCNTs coated with an ordered P3HT layer to enhance the charge separation and transport in the device active layer. Electrical characteristics of devices with SWCNT concentrations up to 40 wt % were measured and are shown to be strongly dependent on the SWCNT loading. A maximum open circuit voltage was measured for SWCNT concentration of 3 wt % with a value of 1.04 V, higher than expected based on the interface band alignment. Modeling of the open-circuit voltage suggests that despite the large carrier mobility in SWCNTs device power conversion efficiency is governed by carrier recombination. Optical characterization shows that only SWCNT with diameter of 1.3–1.4 nm can contribute to the photocurrent with internal quantum efficiency up to 26%. Our results advance the fundamental understanding and improve the design of efficient polymer/SWCNTs solar cells.
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