ZKC

Novel and less toxic quantum dot (QD) semiconductors are desired for developing environmentally benign colloidal quantum dot solar cells. Here, the synthesis of novel lead/cadmium-free neodymium chalcogenide Nd₂(S, Se, Te)₃ QDs via solution-processed method is reported for the first time. The results show that small-bandgap semiconductor QDs with a narrow size distribution ranging from 2 to 8 nm can be produced, and the wide absorption band can be achieved by the redshift owing to the size quantization effect by controlling the initial loading of chalcogenide precursors. By analyzing the band structure of QDs and the energy level alignment between QDs and TiO₂, the influence of energy offset between the conduction band edges of QDs and TiO₂ on the charge transfer dynamics and photovoltaic performance of QD solar cells (QDSCs) is investigated. It is revealed that among the three types of QDs studied, Nd₂Se₃ QDSCs with the smallest energy offset exhibit the best performances and a decent power conversion efficiency of 3.19% is achieved. This work clearly demonstrates the promising potentials of novel rare earth chalcogenide quantum dots in photovoltaic applications.

Lead/cadmium-free and optimized neodymium chalcogenide quantum dots (QDs) have been synthesized by varying the ratio of neodymium to chalcogenide and their promising applications to solar cells have been demonstrated in terms of optical properties, energy level alignment, and charge transfer dynamics, etc. Nd₂Se₃ QDs exhibit a faster charge transfer rate and a conversion efficiency of 3.19% has been achieved.

Delocalized singlet biradical hydrocarbons hold promise as new semiconducting materials for high-performance organic devices. However, to date biradical organic molecules have attracted little attention as a material for organic electronic devices. Here, this work shows that films of a crystallized diphenyl derivative of s-indacenodiphenalene (Ph₂-IDPL) exhibit high ambipolar mobilities in organic field-effect transistors (OFETs). Furthermore, OFETs fabricated using Ph₂-IDPL single crystals show high hole mobility (μ_h = 7.2 × 10⁻¹ cm² V⁻¹ s⁻¹) comparable to that of amorphous Si. Additionally, high on/off ratios are achieved for Ph₂-IDPL by inserting self-assembled mono­layer of alkanethiol between the semiconducting layer and the Au electrodes. These findings open a door to the application of ambipolar OFETs to organic electronics such as complementary metal oxide semiconductor logic circuits.

A singlet biradical nature enables high mobility comparable to that of amorphous Si in organic field-effect transistors (OFETs). This paper focuses on the electronic structure and electrical properties of OFETs of a delocalized singlet biradical hydrocarbon, the diphenyl derivative of s-indacenodiphenalene (Ph₂-IDPL). Ph₂-IDPL holds significant promise as a new semiconducting material for high-performance organic devices.

On page 7064, H.-W. Lin and co-workers demonstrate the use of photovoltaic cells with an organometallic perovskite as the active layer for indoor dim-light energy harvesting. Careful design of the electron transporting materials and fabrication processes allows the traps in the perovskite active layers and carrier dynamics to be controlled. Power conversion efficiencies of ≈20–27% are achieved under 100–1000 lux fluorescent lamp illumination.

Consolidated tables showing an extensive listing of the highest independently confirmed efficiencies for solar cells and modules are presented. Guidelines for inclusion of results into these tables are outlined, and new entries since July 2015 are reviewed. Copyright © 2015 John Wiley & Sons, Ltd.

Consolidated tables showing an extensive listing of the highest independently confirmed efficiencies for solar cells and modules are presented. Guidelines for inclusion of results into these tables are outlined, and new entries since July 2015 are reviewed.

A solution-based passivation scheme is developed featuring the use of molecular iodine and PbS colloidal quantum dots (CQDs). The improved passivation translates into a longer carrier diffusion length in the solid film. This allows thicker solar-cell devices to be built while preserving efficient charge collection, leading to a certified power conversion efficiency of 9.9%, which is a new record in CQD solar cells.

On page 7079, X.-H. Zhang, C.-S. Lee, and co-workers discuss the drawbacks of single-emitting-layer hybrid white organic light-emitting devices (WOLEDs) based on conventional fluorescent hosts, and demonstrate an effective way to overcome these drawbacks by using the thermally activated delayed fluorescent blue exciplex. Based on this new concept, high-efficiency WOLEDs with a forward-viewing power efficiency of 48.7 lm W⁻¹ at 100 cd m⁻² are achieved.

A novel polymer-solar-cell architecture using the conjugated polymer PFS as both the anode and cathode interlayers is constructed, and a high power conversion efficiency of 9.48% is achieved using the corresponding photovoltaic device.

Conjugated small-molecule hole-transport materials (HTMs) with tunable energy levels are designed and synthesized for efficient perovskite solar cells. A champion device with efficiency of 16.2% is demonstrated using a dopant-free DERDTS-TBDT HTM, while the DORDTS-DFBT-HTM-based device shows an inferior performance of 6.2% due to its low hole mobility and unmatched HOMO level with the valence band of perovskite film.

The field of organic electronics is still lacking ubiquitous organic transistors with an efficient electron (n-type) transport that are environmentally and electrically robust. Here, solution-processed n-type N,N′-1H,1H-perfluorobutyldicyanoperylene-carboxydi-imide organic field-effect transistors (OFETs) are reported and it is demonstrated that they are highly stable while operating both in vacuum and in the air at least up to temperatures as high as ≈100 °C. In addition, these crystalline thin-film transistors are found to be resilient to photooxidation under intense illumination in oxygen atmosphere. The performance of these environmentally stable n-type OFETs is on par with the commercial amorphous Si transistors: the highest electron mobility obtained in this study is μ_max ≈ 0.6 cm² V⁻¹ s⁻¹, while the average reproducible mobility is ⟨μ⟩ = 0.4 cm² V⁻¹ s⁻¹. Importantly, no parasitic gate voltage V_G sweep rate dependence of the nominal mobility in these devices is observed. In addition, the charge carrier mobility has been found to be temperature independent in the range T ≈ 250–373 K. The observed great operational stability and resilience against photooxidation, as well as a temperature-independent mobility in these solution-processed n-type OFETs are beneficial for furthering practical applications of organic semiconductor devices.

n-type organic field-effect transistors based on highly crystalline oriented N,N′-1H,1H-perfluorobutyldicyanoperylene-carboxydi-imide films grown from a solution are shown to have an excellent environmental and electrical stability, resistance to photooxidation, and the ability to withstand temperature cycling in a wide temperature range. The charge carrier mobility is found to be temperature independent in the practically relevant range between −25 and 100 °C.

It is commonly believed that the work-function reduction effect of the cathode interfacial material in organic electronic devices leads to better energy-level alignment at the organic/electrode interface, which enhances the device performance. However, there is no agreement on the exact dipole direction in the literature. In this study, a peel-off method to reveal the buried organic/metal interface to examine the energy-level alignment is developed. By splitting the device at different interfaces, it is discovered that oppositely oriented dipoles are formed at different surfaces of the interfacial layer. Moreover, the function of the electrode interface differs in different device types. In organic light-emitting diodes, the vacuum-level alignment generally occurs at the organic/cathode interface, while in organic photovoltaic devices, the Fermi-level pinning commonly happens. Both are determined by the integer charge-transfer levels of the organic materials and the work-function of the electrode. As a result, the performance enhancement by the cathode interfacial material in organic photovoltaic devices cannot be solely explained by the energy-level alignment. The clarification of the energy-level alignment not only helps understand the device operation but also sets up a guideline to design the devices with better performance.

There is no agreement on the dipole direction of the cathode interfacial layer in organic electronic devices in the literature. By splitting the device at different interfaces to study the energy-level alignment, the energetic diagrams of the organic light-emitting diode (OLED) and the organic photovoltaic (OPV) device are clarified. The vacuum level is aligned across the organic/metal interface in OLED, while energy pinning occurs in OPV.

In this work, a thermally and mechanically robust, smooth transparent conductor composed of silver nanowires embedded in a colorless polyimide substrate is introduced. The polyimide is exceptionally chemically, mechanically, and thermally stable. While silver nanowire networks tend not to be thermally stable to high temperatures, the addition of a titania coating on the nano­wires dramatically increases their thermal stability. This allows for the polyimide to be thermally imidized at 360 °C with the silver nanowires in place, creating a smooth (<1 nm root mean square roughness), conductive surface. These transparent conducting substrate-cum-electrodes exhibit a conductivity ratio figure of merit of 272, significantly outperforming commercially available indium-tin-oxide (ITO)-coated plastics. The conductive polymide is subjected to various mechanical tests and is used as a substrate for a thermally deposited, flexible, organic light-emitting diode, which shows improved device performance compared to a control device made on ITO coated glass.

A fully solution processed composite material of a colorless polyimide, titania, and silver nanowires is presented. This material is a new substrate-cum-electrode for optoelectronics devices, which exhibits excellent thermal, mechanical, and chemical stability. A green phosphorescent organic light-emitting diode device fabricated atop this electrode outperforms an indium-tin-oxide-on-glass substrate-cum-electrode control device.

The effects of the incorporation of semiconducting single-walled nanotubes (sc-SWNTs) with high purity on the bulk heterojunction (BHJ) organic solar cell (OSC) based on regioregular poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C₆₁-butyric acid methyl ester (rr-P3HT:PCBM) are reported for the first time. The sc-SWNTs induce the organization of the polymer phase, which is evident from the increase in crystallite size, the red-shifted absorption characteristics and the enhanced hole mobility. By incorporating sc-SWNTs, OSC with a power conversion efficiency (PCE) as high as 4% can be achieved, which is ≈8% higher than our best control device. A novel application of sc-SWNTs in improving the thermal stability of BHJ OSCs is also demonstrated. After heating at 150 °C for 9 h, it is observed that the thermal stability of rr-P3HT:PCBM devices improves by more than fivefold with inclusion of sc-SWNTs. The thermal stability enhancement is attributed to a more suppressed phase separation, as shown by the remarkable decrease in the formation of sizeable crystals, which in turn can be the outcome of a more controlled crystallization of the blend materials on the nanotubes.

Semiconducting single-walled nanotubes (sc-SWNTs) with high purity improve both device performance and thermal stability of organic solar cells based on a blend of a conjugated polymer and a fullerene derivative. The presence of sc-SWNTs induces the organization of the polymer phase, while suppressing the excessive phase separation of the blend materials.

For polymer solar cells (PSCs) with conventional configuration, the vertical composition profile of donor:acceptor in active layer is detrimental for charge carrier transporting/collection and leads to decreased device performance. A cross-linkable donor polymer as the underlying morphology-inducing layer (MIL) to tune the vertical composition distribution of donor:acceptor in the active layer for improved PSC device performance is reported. With poly(thieno[3,4-b]-thiophene/benzodithiophene):[6,6]-phenyl C₇₁-butyric acid methyl ester (PTB7:PC₇₁BM) as the active layer, the MIL material, PTB7-TV, is developed by attaching cross-linkable vinyl groups to the side chain of PTB7. PSC device with PTB7-TV layer exhibits a power conversion efficiency (PCE) of 8.55% and short-circuit current density (J_SC) of 15.75 mA cm⁻², in comparison to PCE of 7.41% and J_SC of 13.73 mA cm⁻² of the controlled device. The enhanced device performance is ascribed to the much improved vertical composition profile and reduced phase separation domain size in the active layer. These results demonstrate that cross-linked MIL is an effective strategy to improve photovoltaic performance of conventional PSC devices.

A cross-linkable donor polymer is developed and used as the underlying layer to improve the vertical composition distribution of donor:acceptor in the active layer of polymer solar cells (PSCs). With the improvement, the regular PSC device based on PTB7:PC₇₁BM active layer exhibits power conversion efficiency increase from 7.41% to 8.55%.