wangzhaowei

A new series of organic salts with selective near-infrared (NIR) harvesting to 950 nm is reported, and anion selection and blending is demonstrated to allow for fine tuning of the open-circuit voltage. Extending photoresponse deeper into the NIR is a significant challenge facing small molecule organic photovoltaics, and recent demonstrations have been limited by open-circuit voltages much lower than the theoretical and practical limits. This work presents molecular design strategies that enable facile tuning of energy level alignment and open-circuit voltages in organic salt-based photovoltaics. Anions are also shown to have a strong influence on exciton diffusion length. These insights provide a clear route toward achieving high efficiency transparent and panchromatic photovoltaics, and open up design opportunities to rapidly tailor molecules for new donor–acceptor systems.

Organic salt photovoltaics with open-circuit voltages approaching the excitonic limit are demonstrated. Anion exchange is shown to enhance energy level alignment and nearly double the exciton diffusion length. Anion alloying enables a design strategy for fine energy level tuning to simultaneously optimize open-circuit voltage and photocurrent in new organic salt systems for multijunction and transparent phovoltaics with deeper near-infrared response.

Partially converted poly(1,4-phenylenevinylene) (PPV) is used as a thin p-type interlayer in planar organohalide pervoskite solar cells resulting in a high V_oc, 1.06 V, a power conversion efficiency of ≈15%, and minimized charge carrier recombination.

A TiO₂|Co₃O₄|MoO₃ all-oxide solar cell produced by spray pyrolysis and pulsed laser deposition (PLD) onto a fluorine-doped tin-oxide (FTO) glass substrate with gold (Au) back contacts is demonstrated for the first time. A combinatorial approach is implemented to study the effect of molybdenum oxide (MoO₃) as a recombination contact and the influence of the cobalt oxide (Co₃O₄) light-absorber thickness on the performance of the solar cells. An increase of more than 200 mV in the open circuit voltage (V_oc) is observed with a concurrent enhancement in terms of short-circuit current (J_sc) and maximum power in comparison with TiO₂|Co₃O₄ devices without the MoO₃ layer. To understand the mechanism, full drift diffusion simulations are performed. The higher performance is attributed to elimination of a recombination process at the absorber/metal back-contact interface and surface passivation by the MoO₃ layer.

A combinatorial study with advanced modelling demonstrates that MoO₃ is a very efficient hole-transport material for TiO₂|Co₃O₄|MoO₃|Au all-oxide solar cells because it eliminates the surface recombination at the absorber/metal back-contact interface.

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 efficiencies exceeding 3% over device areas of ≈1 mm², large-area SWCNT solar cells have not yet been demonstrated. In particular, with increasing device area, spatial inhomogeneities in the SWCNT film have limited overall device performance. Here, 1,8-diiodooctane (DIO) is utilized as a solvent additive to reduce fullerene domain size and to improve SWCNT–fullerene bulk-heterojunction morphology. Under optimized conditions, DIO elucidates the influence of SWCNT chiral distribution on overall device performance, revealing a tradeoff between short-circuit current density and fill factor as a function of the chirality distribution present. The combination of SWCNT chirality distribution engineering and improved spatial homogeneity via solvent additives enables area-scaling of SWCNT–fullerene solar cells with performance comparable to small-area cells.

Solvent additives enable large-area carbon nanotube solar cells by reducing spatial inhomogeneities within the carbon nanotube–fullerene active layer. These additives also reveal the impact of carbon nanotube chiral distribution on performance and enable the fabrication of large-area carbon nanotube solar cells with power conversion efficiencies comparable to small-area cells.

Charge extracting layers play a key role in the elimination of hysteresis from J–V characteristics of inverted hybrid perovskite solar cells. Methanofullerene electron extracting layers stabilize short-circuit photocurrents from the very first J–V scan, while preconditioning cycles are needed to stabilize the open-circuit voltage owing to interaction between migrating iodide ions and the charge extraction layer.

The role of excess excitation energy on long-range charge separation in organic donor/acceptor bulk heterojunctions (BHJs) continues to be unclear. While ultrafast spectroscopy results argue for efficient charge separation through high-energy charge-transfer (CT) states within the first picosecond (ps) of excitation, charge collection measurements suggest excess photon energy does not increase the current density in BHJ devices. Here, the population dynamics of charge-separated polarons upon excitation of high-energy polymer states and low-energy interfacial CT states in two polymer/fullerene blends from ps to nanosecond time scales are studied. It is observed that the charge-separation dynamics do not show significant dependence on excitation energy. These results confirm that excess exciton energy is not necessary for the effective generation of charges.

Ultrafast spectroscopy unravels the role of excess excitation energy on charge separation in organic photovoltaic solar cells. Comparison of the polaron and charge-transfer (CT) state populations after selective excitation of the high-energy polymer states and lowest energy CT states shows that excess exciton energy is not necessary for the effective generation of charges.

Water ingress represents one of the major reliability concerns for the fabrication, storage, and operation of organic photovoltaic devices. In article number 1501065, Jens Adams and co-workers track water-induced photovoltaic degradation in organic solar cells using full frame thermographic and electroluminescence imaging and present a diffusion model for predicting the propagation of water in encapsulated devices. Cover design by George Spyropoulos.

In article number 1500721, Jinsong Huang and co-workers report that ion migration can be driven by illumination-induced photovoltage in hybrid perovskite solar cells. As a result of photo-induced ion migration, both the power conversion efficiency and stability of perovskite solar cells are improved.

2D nanomaterials have been found to show surface-dominant phenomena and understanding this behavior is crucial for establishing a relationship between a material's structure and its properties. Here, the transition of molybdenum disulfide (MoS₂) from a diffusion-controlled intercalation to an emergent surface redox capacitive behavior is demonstrated. The ultrafast pseudocapacitive behavior of MoS₂ becomes more prominent when the layered MoS₂ is downscaled into nanometric sheets and hybridized with reduced graphene oxide (RGO). This extrinsic behavior of the 2D hybrid is promoted by the fast Faradaic charge-transfer kinetics at the interface. The heterostructure of the 2D hybrid, as observed via high-angle annular dark field–scanning transmission electron microscopy and Raman mapping, with a 1T MoS₂ phase at the interface and a 2H phase in the bulk is associated with the synergizing capacitive performance. This 1T phase is stabilized by the interactions with the RGO. These results provide fundamental insights into the surface effects of 2D hetero-nanosheets on emergent electrochemical properties.

The extrinsic surface charge-storage behavior of 2D RGO/MoS₂ hybrids translated from diffusion-controlled intercalation mechanism is demonstrated. The 2D RGO/MoS₂ hybrids exhibit a 1T phase of MoS₂ at the interface interacting with the RGO sheets, where the Faradaic charge-transfer process is facilitated by the strong interplay between the redox-active MoS₂ and electrically conductive RGO sheets.

The global energy demand is increasing at the same time as fossil fuel resources are dwindling. Consequently, the search for alternative energy sources is a major topic worldwide. Solar energy is one of the most promising, effective and emission-free energy sources. However, the energy has to be stored to compensate the fluctuating availability of the sun and the actual energy demand. Photo-rechargeable electric energy storage systems may solve this problem by immediately storing the generated electricity. Different combinations of solar cells and storage devices are possible. High efficiencies can be achieved by the combination of dye-sensitized solar cells (DSSC) and capacitors. However, other hybrid devices including DSSCs or organic photovoltaic systems and redox flow batteries, lithium ion batteries and metal air batteries are playing an increasing role in this research field. This Progress Report reviews the state of the art research of photo-rechargeable batteries based on organic solar cells, as well as storage modules.

Recent developments in the investigation of solar rechargeable electric energy storage systems are reviewed. Details of operation and performance are provided for organic hybrid devices of different solar cell types (e.g., dye sensitized solar cells or bulk heterojunction solar cells) and several energy storage systems (e.g., supercapacitors, redox flow batteries or metal air batteries).