ZiQi Sun

The synthesis and characterization of a series of novel small-molecule hole-transporting materials (HTMs) based on an anthra[1,2-b:4,3-b′:5,6-b′′:8,7-b′′′]tetrathiophene (ATT) core are reported. The new compounds follow an easy synthetic route and have no need of expensive purification steps. The novel HTMs are tested in perovskite solar cells and power conversion efficiencies (PCE) of up to 18.1% under 1 sun irradiation are measured. This value is comparable with the 17.8% efficiency obtained using 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene as a reference compound. Similarly, a significant quenching of the photoluminescence in the first nanosecond is observed, indicative of effective hole transfer. Additionally, the influence of introducing aliphatic alkyl chains acting as solubilizers on the device performance of the ATT molecules is investigated. Replacing the methoxy groups on the triarylamine sites by butoxy-, hexoxy-, or decoxy-substituents greatly improves the solubility of the compounds without changing the energy levels, yet at the same time significantly decreasing the conductivity as well as the PCE, 17.3% for ATT-OBu, 15.7% for ATT-OHex, and 9.7% for ATT-ODec.

A sulfur-rich polycyclic aromatic hydrocarbon with a flat and rigid π-conjugated structure endowed with triarylamine groups is synthesized for highly efficient perovskite solar cells. The influence of alkyl chains, often introduced to increase the solubility of the hole-transporting materials, is furthermore investigated. Efficiencies as high as 18.1% are obtained.

Intrinsic photodegradation of organic solar cells, theoretically attributed to CH bond rearrangement/breaking, remains a key commercialization barrier. This work presents, via dark electron paramagnetic resonance (EPR), the first experimental evidence for metastable C dangling bonds (DBs) formed by blue/UV irradiation of polymer:fullerene blend films in nitrogen. The DB density increases with irradiation and decreases ≈4-fold after 2 weeks in the dark. The dark EPR also shows increased densities of other spin-active sites in photodegraded polymer, fullerene, and polymer:fullerene blend films, consistent with broad electronic measurements of fundamental properties, including defect/gap state densities. The EPR and electronic measurements enable identification of defect states, whether in the polymer, fullerene, or at the donor/acceptor (D/A) interface. Importantly, the EPR results indicate that the DBs are at the D/A interface, as they were present only in the blend films. The role of polarons in interface DB formation is also discussed.

For the first time, strong electron paramagnetic resonance evidence is provided that irradiation of bulk heterojunction polymer:fullerene solar cells by blue and shorter wavelength photons (<495 nm), likely assisted by highly energized (“hot”) polarons, generates C dangling bonds at the polymer:fullerene interfaces. This photodegradation process may be one of the key obstacles to commercialization of such cells.

Device stability of planar perovskite solar cells is improved by virtue of multifunctional BQ additive. The morphology and crystal quality of the perovskite films are improved because BQ slows the rate of perovskite crystal formation. Electron transfer from perovskite to BQ reduces charge-recombination losses, and the oxidizing ability of BQ effectively suppresses the formation of metallic lead and improves device lifetime.

Ionic iridium(III) complexes are emerging with great promise for organic electronic devices, owing to their unique features such as ease of molecular design and synthesis, excellent photophysical properties, superior redox stability, and highly efficient emissions of virtually all colors. Here, recent progress on new material design, regarding photo- and electroluminescence is highlighted, including several interesting topics such as: i) color-tuning strategies of cationic iridium(III) complexes, ii) widespread utilization in phosphorescent light-emitting devices fabricated by not only solution processes but also vacuum evaporation deposition, and iii) potential applications in data record, storage, and sercurity. Results on anionic iridium(III) complexes and “soft salts” are also discussed, indicating a new related subject. Finally, a brief outlook is suggested, pointing out that ionic iridium(III) complexes should play a more significant role in future organic electronic materials technology.

Ionic iridium(III) complexes show high promise for organic electronic devices owing to their excellent luminescence of virtually all colors. Recent progress on material design, characterization, and applications of ionic iridium(III) complexes is highlighted, pointing out their great potential for future organic displays, lighting, and data record storage.

Integration of organic/inorganic hybrid perovskites with metallic or semiconducting phases of 2D MoS₂ nanosheets via solution processing is demonstrated. The results show that the collection of charge carriers is strongly dependent on the electronic properties of the 2D MoS₂ with metallic MoS₂ showing high responsivity and the semiconducting phase exhibiting high on/off ratios.

Multijunction solar cells promise higher power-conversion efficiency than the single-junction. With respect to two-terminal devices, an accurate measurement of the spectral response requires a delicate adjustment of the light- and voltage-biasing; otherwise it can result in artifacts in the data and thus misinterpretation of the cell properties. In this paper, the formation of measurement artifacts is analyzed by modeling the measurement process, that is, how the current–voltage characteristics of the component subcells evolve with the photoresponse to the incident spectrum. This enables the examination on the operation conditions of the subcells, offering additional information for the study of artifacts. In particular, the influence of shunt resistance, bias-light intensity, and bias voltage on the measurement is examined. Having observed the dynamics and vulnerability of the measurement, the proper ways to configure and interpret a measurement are discussed in depth. As a practical example, simulations of the measurements on a quadruple-junction thin-film silicon solar cell demonstrate that the modeling can be used to interpret eventual irregularities in the measured spectral response. The application of such tool is especially meaningful taking account of the diverse and rapid development of novel hybrid multijunction solar cells, in which the role of reliable characterizations is essential.

The formation of artifacts in the spectral response measurement of two-terminal multijunction solar cells is visually revealed by changing the cell properties and bias conditions in modeling. The simulations greatly help to understand the origins of artifacts, and to avoid the pitfall of misinterpreting the measured data, making the research in novel hybrid multijunction solar cells more reliable.

Searching for a new material to build the next-generation rechargeable lithium-ion batteries (LIBs) with high electrochemical performance is urgently required. Owing to the low-cost, non-toxicity, and high-safety, the family of manganese oxide including the Na-Mn-O system is regarded as one of the most promising electrode materials for LIBs. Herein, a new strategy is carried out to prepare a highly porous and electrochemically active Na_0.55Mn₂O₄·1.5H₂O (SMOH) compound. As an anode material, the Na-Mn-O nanocrystal material dispersed within a carbon matrix manifests a high reversible capacity of 1015.5 mA h g⁻¹ at a current density of 0.1 A g⁻¹. Remarkably, a considerable capability of 546.8 mA h g⁻¹ remains even after 2000 discharge/charge cycles at the higher current density of 4 A g⁻¹, indicating a splendid cyclability. The exceptional electrochemical properties allow SMOH to be a promising anode material toward LIBs.

Rational Na_0.55M₂O₄•1.5H₂O (SMOH) nanocrystals homogeneously dispersed within an amorphous carbon matrix are synthesized for the first time. When used as anode material for lithium-ion batteries, they exhibit an outstanding reversible specific capacity (≈1016 mA h g^–1 at 0.1 A g^–1) and a splendid cyclability (a reversible capacity of ≈547 mA h g^–1 remains even after 2000 discharge/charge cycles at the higher current density of 4 A g^–1).

On page 9713, L. Gu, Z. Fan and co-workers, for the first time, report the large-scale growth of ultra-high density, well-ordered lead halide perovskite nanowires, using a vapor reaction method. The geometry of the nanowires can be precisely engineered, thus they are highly promising for integrated nano-electronics/optoelectronics. Using these nanowires, proof-of-concept image sensors with 1,024 pixels are fabricated and their functionality is demonstrated.

C.-Z. Li, H. Chen and co-workers present, on page 9729, for the first time, efficient non-fullerene tandem organic solar cells (OSCs) by utilizing all non-fullerene acceptor-based bulk heterojunctions as sub-cells. A high power conversion efficiency of 8.48% is achieved with an ultra-high open-circuit voltage of 1.97 V, which is the highest voltage value reported to date feasible for water splitting among the efficient tandem OSCs.

MACl, as additive to the standard FAPbI₃ precursor solution, enables near-complete coverage perovskite film to stabilize the phase-pure black FAPbI₃ annealing at 100 °C. A partial substitution of FACl for FAI in precursor solution is used to grow FA perovskites with controllable chlorine doped fraction, which improves the performance of the planar perovskite solar cell.

A PbSe quantum dot solar cell with an efficiency of 7.22% and a fill factor of 62.4% is achieved by applying a CsPbBr₃ perovskite quantum dot back layer. The back layer can effectively suppress carrier recombination at the PbSe/Au interfaces, hence lead to significant improvement in open-circuit voltage and fill factor.

Transformation of unipolar n-type semiconductor behavior to ambipolar and finally to unipolar p-type behavior in CH₃NH₃PbI₃ microplate field-effect transistors by thermal annealing is reported. The photoluminescence spectra essentially maintain the same features before and after the thermal annealing process, demonstrating that the charge transport measurement provides a sensitive way to probe low-concentration defects in perovskite materials.

Using two-photon tomography, carrier lifetimes are mapped in polycrystalline CdTe photovoltaic devices. These 3D maps probe subsurface carrier dynamics that are inaccessible with traditional optical techniques. They reveal that CdCl₂ treatment of CdTe solar cells suppresses nonradiative recombination and enhances carrier lifetimes throughout the film with substantial improvements particularly near subsurface grain boundaries and the critical buried p–n junction.