Semiconducting single-walled carbon nanotube/fullerene bulk heterojunctions exhibit unique optoelectronic properties highly suitable for flexible, efficient, and robust photovoltaics and photodetectors. We investigate charge-transfer dynamics in inverted devices featuring a polyethylenimine-coated ZnO nanowire array infiltrated with these blends and find that trap-assisted recombination dominates transport within the blend and at the active layer/nanowire interface. We find that electrode modifiers suppress this recombination, leading to high performance.

Alkaline-earth zirconates (CaZrO3, SrZrO3, and BaZrO3) are under active investigation as solid-state electrolytes in hydrogen fuel cells. Their performance as proton conductors depends critically on the properties of acceptor dopants. Here, we use first-principles calculations to study the role of acceptors and point defects in incorporating protons through an oxygen-vacancy-mediated process. For CaZrO3, we find that ZrCa antisites suppress formation of oxygen vacancies. Other intrinsic point defects are shown not to hinder performance. Common unintentional impurities, such as N and C, are not good acceptors but can incorporate in other configurations. Our results show that the effectiveness of common dopants such as Sc and Y is limited by self-compensation due to their incorporation on the “wrong” cation site, where they act as donors. We demonstrate that using alkali metal dopants overcomes this problem, as the formation energy of compensating donors is very high. Alkali metal dopants also have low binding energies for protons, reducing their tendency to act as traps and hence enhancing proton conductivity. Our guidelines for choosing acceptor dopants and optimizing synthesis conditions can greatly improve the efficacy of these proton-conducting oxides as solid-state electrolytes.

blends have recently demonstrated power conversion effi ciencies (PCEs) as high as 3.1% (2.5% NREL certifi ed) for device areas of 0.06-1.2 mm 2 . [7][8][9][10][11][12][13] These devices show excellent ambient stability and nearinfrared (NIR) absorption, [ 11 ] in contrast to other widely researched organic and perovskite photovoltaic technologies. [ 14,15 ] Despite these advances, SWCNT-fullerene solar cells have to date failed to demonstrate high performance over device areas larger than ≈1 mm 2 . In contrast, other TFPV technologies are routinely demonstrated at areas of 6 mm 2 and above. [ 15,16 ] Importantly, SWCNT-fullerene solar cells must maintain performance over areas on par with other TFPV technologies in order to exploit their exceptional absorption and chemical stability in hybrid or tandem photovoltaics, where an SWCNT-fullerene subcell would add value by harvesting NIR light and slowing degradation. Recently, it has been shown that trap-assisted recombination within the active layer limits performance in SWCNT-fullerene solar cells. [ 17 ] This recombination is in part due to the spatial inhomogeneities resulting from fullerene or SWCNT aggregates within the BHJ active layer. Such aggregates decrease the interfacial area between the donor and acceptor domains, limiting effi cient exciton dissociation and charge extraction. These aggregates also provide conductive pathways between both electrodes that electrically short the cell and limit both shortcircuit current density ( J sc ) and open-circuit voltage ( V oc ). [ 18 ] As the solar cell areas are increased, these negative effects begin to dominate the overall device performance, oftentimes with catastrophic consequences.Here, we report improved BHJ morphology and the resulting large-area device performance by incorporating the solvent additive 1,8-diiodooctane (DIO) within the SWCNT-fullerene active layer. DIO has previously been used as an additive in polymer solar cells and is known to break apart PC 71 BM aggregates, [ 16,19 ] which can have tremendous impact on solar cell performance. [ 20 ] We systematically vary the DIO concentration in the SWCNT-fullerene blend, fi nding that an optimal concentration of 1 vol% DIO enables large-area device performance that is comparable to smaller area devices. Atomic force microscopy (AFM) reveals that the addition of DIO signifi cantly reduces the Single-walled carbon nanotube (SWCNT) fullerene solar cells have recently attracted attention due to their low-cost processing, high environmental stability, and near-infrared absorption. While SWCNT-fullerene bulk-heterojunction photovoltaics employing an inverted architecture and polychiral SWCNTs have achieved effi ciencies exceeding 3% over device areas of ≈1 mm 2 , large-area SWCNT solar cells have not yet been demonstrated. In particular, with increasing device area, spatial inhomogeneities in the SWCNT fi lm have limited overall device performance. Here, 1,8-diiodooctane (DIO) is utilized as a solvent additive to reduce fullerene domain size and to impro...

Solid-state metal hydrides are prime candidates to replace compressed hydrogen for fuel cell vehicles due to their high volumetric capacities. Sodium aluminum hydride has long been studied as an archetype for higher-capacity metal hydrides, with improved reversibility demonstrated through the addition of titanium catalysts; however, atomistic mechanisms for surface processes, including hydrogen desorption, are still uncertain. Here, operando and ex situ measurements from a suite of diagnostic tools probing multiple length scales are combined with ab initio simulations to provide a detailed and unbiased view of the evolution of the surface chemistry during hydrogen release. In contrast to some previously proposed mechanisms, the titanium dopant does not directly facilitate desorption at the surface. Instead, oxidized surface species, even on well-protected NaAlH 4 samples, evolve during dehydrogenation to form surface hydroxides with differing levels of hydrogen saturation. Additionally, the presence of these oxidized species leads to considerably lower computed barriers for H 2 formation compared to pristine hydride surfaces, suggesting that oxygen may actively participate in hydrogen release, rather than merely inhibiting diffusion as is commonly presumed. These results demonstrate how close experiment−theory feedback can elucidate mechanistic understanding of complex metal hydride chemistry and potentially impactful roles of unavoidable surface impurities.