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o-Chlorobenzaldehyde (CBA) is a derivative of chlorobenzene (CB). The boiling point of CBA is 212 °C, much lower than 332 °C for 1,8-diiodooctane (DIO). With CBA as solvent additive in CB host solvent, CBA could be fast removed during spin-coating 100, 200, and 300 nm thick thieno[3,4-b]thiophene/benzodithiophene polymer (PTB7):[6,6]-phenyl C₇₁-butyric acid methyl ester (PC₇₁BM) active layers, achieving power conversion efficiencies of 9.11%, 8.24%, and 7.11%, respectively, much higher than 7.53%, 5.71%, and 4.93% for corresponding DIO control devices with vacuum drying.

In article number 1600637, Alan J. Heeger, Han Young Woo, Jin Young Kim, and co-workers demonstrate high performance ternary blend polymer solar cells including two donor polymers which share the same polymeric backbone. Real charge carrier behavior of ternary blends is firstly clarified via transient absorption spectroscopy as parallel bulk-heterojunction.

Using small amounts of solvent additives during fabrication of organic solar cells has been formerly shown to render a facile approach for improving the performance by tuning the active layer nano-morphology. However, in certain cases, solvent additives are now found to accelerate device degradation. This is reported by Peter Müller-Buschbaum and co-workers in article number 1600712. Cover image by Christoph Hohmann, Nano-systems Initiative Munich (NIM).

Organic solar cells (OSCs) are lightweight, have adaptable colors, and can be produced in low-cost procedures on transparent and flexible surfaces. This makes them attractive for markets in which other technologies cannot compete, for example in architectural and consumer product integration. However, both efficiencies and long term operational stability of OSCs do not yet meet the standards set by their inorganic counterparts. This review compiles the growing knowledge about how nanostructured carbon materials, such as fullerenes and carbon nanotubes, decisively influence the operational stability of organic photovoltaics. Firstly, important degradation pathways are introduced and a differential detection scheme is set up to find the dominant loss channel by means of state-of-the-art characterization methods. Then, fullerenes ability to both stabilize and destabilize the donor polymer against photooxidation via different mechanisms (e.g., inner filter effect or radical scavenging) is examined in detail. The “burn-in” problem, an initial rapid efficiency loss in PC₆₀BM-based OSCs, is shown to derive from light-induced PC₆₀BM dimerization, an effect that can also be positively exploited to reduce thermal degradation. Finally, thermal stabilization via additional approaches involving the fullerene derivative, such as crosslinking or incorporation into block copolymers, is presented.

Carbon nanostructures, particularly fullerene derivatives, possess the ability to act as radical scavengers and undergo photodimerization, consequently influencing the photochemical and morphological degradation of the active layer. These properties can be exploited to produce organic solar cells with longer operational lifetimes without compromising device efficiency and manufacturing costs.

Solution-processed organic solar cells with promising photovoltaic performance and extraordinary high thermal stability are achieved by employing novel fullerene-based acceptors in combination with two state-of-the-art polymer donors. The findings demonstrated in this work underline the necessity and importance of novel acceptor design rules for highly efficient organic solar cells with excellent device stability.

In article number 1601055, Jooho Moon and co-workers demonstrate efficient semitransparent solar cells based on vertically aligned, one dimensional organic-inorganic hybrid perovskite using anodized aluminium oxide (AAO) scaffold. This nano-structuring facilitates achieving the record efficiency of 9.6% at the high average visible transmittance of 33.4%, with the advantages of anti-reflection effect by AAO template on compact TiO₂ layer and vertically restricted carrier transport at nano-pillar perovskite.

A growth-temperature-mediated two-step chemical vapor deposition strategy is designed to synthesize MoS₂/WS₂ and WS₂/MoS₂ stacks on Au foils. Predominantly A–A stacked MoS₂/WS₂ and A–B stacked WS₂/MoS₂ are selectively achieved and confirmed. Relative enhancements or reductions in photocatalytic activities of MoS₂/WS₂ or WS₂/MoS₂ are observed under illumination, because the type-II band alignment enables directional electron flow from electrode to active site.

Morphology control is one of the key strategies in optimizing the performance of organic photovoltaic materials, particularly for diketopyrrolopyrrole (DPP)-based donor polymers. The design of DPP-based polymers that provide high power conversion efficiency (PCE) presents a significant challenge that requires optimization of both energetics and morphology. Herein, a series of high performance, small band gap DPP-based terpolymers are designed via two-step side chain engineering, namely introducing alternating short and long alkyls for reducing the domain spacing and inserting alkylthio for modulating the energy levels. The new DPP-based terpolymers are compared to delineate how the side chain impacts the mesoscale morphology. By employing the alkylthio-substituted terpolymer PBDPP-TS, the new polymer solar cell (PSC) device realizes a good balance of a high V_oc of 0.77 V and a high J_sc over 15 mA cm⁻², and thus realizes desirable PCE in excess of 8% and 9.5% in single junction and tandem PSC devices, respectively. The study indicates better control of domain purity will greatly improve performance of single junction DPP-based PSCs toward 10% efficiency. More significantly, the utility of this stepwise side chain engineering can be readily expanded to other classes of well-defined copolymers and triggers efficiency breakthroughs in novel terpolymers for photovoltaic and related electronic applications.

A new class of small band gap terpolymers featuring diketopyrrolopyrrole unit are designed and their mesoscale morphology are well-correlated with device characteristics. The alkylthio-substituted terpolymer PBDPP-TS exhibits deep highest occupied molecular orbital energy level and optimal domain characteristic length/domain purity, resulting in over 8% and 9.5% efficiency for single junction and tandem polymer solar cells, respectively.

The extent to which the soft structural properties of metal halide perovskites affect their optoelectronic properties is unclear. X-ray diffraction and micro-photoluminescence measurements are used to show that there is a coexistence of both tetragonal and orthorhombic phases through the low-temperature phase transition, and that cycling through this transition can lead to structural changes and enhanced optoelectronic properties.

Scanning nanofocus X-ray diffraction (nXRD) performed at a synchrotron is used to simultaneously probe the morphology and the structural properties of spin-coated CH₃NH₃PbI₃ (MAPI) perovskite films for photovoltaic devices. MAPI films are spin-coated on a Si/SiO₂/poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) substrate held at different temperatures during the deposition in order to tune the perovskite film coverage. The films are then investigated using nXRD and scanning electron microscopy (SEM). The advantages of nXRD over SEM and other techniques are discussed. A method to visualize, selectively isolate, and structurally characterize single perovskite grains buried within a complex, polycrystalline film is developed. The results of nXRD measurements are correlated with solar cell device measurements, and it is shown that spin-coating the perovskite precursor solution at elevated temperatures leads to improved surface coverage and enhanced solar cell performance.

Scanning nanofocus X-ray diffraction is used to simultaneously probe the morphology and the structural properties of spin-coated CH₃NH₃PbI₃ perovskite films. The technique allows for perovskite grain segmentation based on a variety of structural properties and is used to understand why spin-coating the perovskite precursor solution at elevated temperature leads to improved surface coverage and enhanced solar cell performance.

On page 7084, P. Müller-Buschbaum and co-workers report the fabrication of dye-free hybrid solar cells based on hierarchically structured titania films and poly(3-hexylthiophene) at low temperature. This type of cells has unique advantages with respect to low cost and energy efficiency. The hierarchical structures of titania are beneficial for enhancing light harvesting in the hybrid solar cells, thereby improving device performance. Cover image by Christoph Hohmann, Nano-systems Initiative Munich (NIM).

A bimodal texturing effect of semiconducting polymers is investigated by incorporating conjugated small molecules to significantly improve the charge transport characteristics via formation of 3D transport pathways. Solution blending of the electron-transporting polymer, poly{[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} (P(NDI2OD-T2)), with small molecular crystals of tetrathiafulvalene and tetracyanoquinodimethane is used, and the thin film microstructures are studied using a combination of atomic force microscopy, transmission electron microscopy, 2D grazing incidence X-ray diffraction, and surface-sensitive near-edge X-ray absorption fine structure. Blended thin films show edge-on and face-on bimodal texture with long-range order and microstructure packing orientation preferable for electron transport through the channel in organic field-effect transistors, which is confirmed by high electron mobility 1.91 cm² V⁻¹ s⁻¹, small contact resistance, and low energetic disorder according to temperature dependence of the field-effect mobility. Structural changes suggest a 3D network charge transport model via lamella packing and bimodal orientation of the semiconducting polymers.

Polymer morphology and molecular orientation are significantly changed by introducing conjugated planar small molecules into semiconducting polymer films. Face-on and edge-on bimodal texture with better long-range arrangement and ordered lamellar stacking enhances efficient charge transport in the polymer semiconductor of organic field-effect transistors.

Cesium lead halide quantum dots (QDs) have tunable photoluminescence that is capable of covering the entire visible spectrum and have high quantum yields, which make them a new fluorescent materials for various applications. Here, the synthesis of CsPbX₃ (X = Cl, Br, I, or mixed Cl/Br and Br/I) QDs by direct ion reactions in ether solvents is reported, and for the first time the synergetic effects of solvent polarity and reaction temperature on the nucleation and growth of QDs are demonstrated. The use of solvent with a low polarity enables controlled growth of QDs, which facilitates the synthesis of high-quality CsPbX₃ QDs with broadly tunable luminescence, narrow emission width, and high quantum yield. A QD white LED (WLED) is demonstrated by coating the highly fluorescent green-emissive CsPbBr₃ QDs together with red phosphors on a blue InGaN chip, which presents excellent warm white light emission with a high rendering index of 93.2 and color temperature of 5447 K, suggesting the potential applications of highly fluorescent cesium lead halide perovskite QDs as an alternative color converter in the fabrication of WLEDs.

CsPbX₃ quantum dots (QDs) have superior photophysics properties, including high quantum yield (up to 72%), wide color gamut (>NTSC standard), and narrow emission width (18–38 nm). The WLED based on CsPbBr₃ QDs present excellent warm white light emission with a high rendering index of 93.2 and CIE coordinate of (0.3339, 0.3617).

Hybrid perovskite and all-inorganic perovskite have attracted much attention in recent years owing to their successful use in the photovoltaic field. Usually the perovskite is used in its bulk form, although recently, perovskites' nanocrystalline form has received increased attention. Recent developments in the evolving research field of nanomaterial-based perovskite are reviewed. Both hybrid organic-inorganic and all-inorganic perovskite nanostructures are discussed, as well as approaches to tune the optical properties by controlling the size and shape of perovskite nanostructures. In addition, chemical modifications can change the perovskite nanostructures' band-gap, similar to their bulk counterpart. Several applications, including light-emitting diodes, lasers, and detectors, demonstrate the latent potential of perovskite nanostructures.

Recent developments in the evolving research field of nanomaterial-based perovskite are reviewed. Both hybrid organic-inorganic and all-inorganic perovskite nanostructures are discussed, as well as approaches to tune the optical properties by controlling the size and the shape of the perovskite nanostructures. Several applications, including light-emitting diodes, lasers, and detectors, demonstrate the latent potential of perovskite nanostructures.

A robust and expedient gas quenching method is developed for the solution deposition of hybrid perovskite thin films. The method offers a reliable standard practice for the fabrication of a non-exhaustive variety of perovskites exhibiting excellent film morphology and commensurate high performance in both regular and inverted structured solar cell architectures.

A simple yet general swelling–deswelling microencapsulation strategy has been developed to achieve well dispersed and intimately passivated crystalline organic–inorganic perovskites nanoparticles within polymer matrixes and results in a series of highly luminescent CH₃NH₃PbBr₃ (MAPbBr₃)–polymer composite films with unprecedented water and thermal stabilities and superior color purity.

The charge-carrier balance strategy by interface engineering is employed to optimize the charge-carrier transport in inverted planar heterojunction perovskite solar cells. N,N-Dimethylformamide-treated poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and poly(methyl methacrylate)-modified PCBM are utilized as the hole and electron selective contacts, respectively, leading to a high power conversion efficiency of 18.72%.