Ligand-Nondestructive Direct Photolithography Assisted by Semiconductor Polymer Cross-Linking for High-Resolution Quantum Dot Light-Emitting Diodes.

The photolithographic patterning of fine quantum dot (QD) films is of great significance for the construction of QD optoelectronic device arrays. However, the photolithography methods reported so far either introduce insulating photoresist or manipulate the surface ligands of QDs, each of which has negative effects on device performance. Here, we report a direct photolithography strategy without photoresist and without engineering the QD surface ligands. Through cross-linking of the surrounding semiconductor polymer, QDs are spatially confined to the network frame of the polymer to form high-quality patterns. More importantly, the wrapped polymer incidentally regulates the energy levels of the emitting layer, which is conducive to improving the hole injection capacity while weakening the electron injection level, to achieve balanced injection of carriers. The patterned QD light-emitting diodes (with a pixel size of 1.5 µm) achieve a high external quantum efficiency of 16.25% and a brightness of >1.4 × 105 cd/m2. This work paves the way for efficient high-resolution QD light-emitting devices.

Approaching the Fill Factor Limit in Dopant-Free Hole Transporting Layer-Based All-Inorganic Perovskite Solar Cells.

As an important part of perovskite solar cells (PSCs), hole transporting layer (HTL) has a critical impact on the performance and stability of the devices. In an attempt to alleviate the moisture and thermal stability issues from the commonly used HTL Spiro-OMeTAD with dopant, it is urgent to develop novel HTLs with high stability. In this study, a new class of polymers D18 and D18-Cl are applied as undoped HTL for CsPbI2Br-based PSCs. In addition to the excellent hole transporting properties, we unveil that D18 and D18-Cl with larger thermal expansion coefficient than that of CsPbI2Br could impose a compressive stress onto the CsPbI2Br film upon thermal treatment, which could release the residual tensile stress in the film. As a result, the efficiency of CsPbI2Br-based PSCs with D18-Cl as HTL reaches 16.73%, and the fill factor (FF) exceeds 85%, which is one of the highest FF records for the conventional-structured device to date. The devices also show impressive thermal stability with over 80% of the initial PCE retained after 85 °C heating for 1500 h.

Asymmetric Substitution of End-Groups Triggers 16.34% Efficiency for All-Small-Molecule Organic Solar Cells.

Asymmetric substitution of end-groups is first applied in molecular donors. Three commonly used end-groups of 2-ethylhexyl cyanoacetate (CA), 2-ethylhexyl rhodanine (Reh), and 1H-indene-1,3(2H)-dione (ID) are combined to construct a series of symmetric and asymmetric donors. Correspondingly, the asymmetric donors SM-CA-Reh and SM-CA-ID show largely increased dipole moments (2.14 and 3.39 D, respectively) and enhanced aggregation propensity, as compared to those of symmetric donors of SM-CA, SM-Reh, and SM-ID. Using N3 as acceptor, interestingly, SM-CA-Reh integrates the photovoltaic characteristics of high fill factor (FF) for SM-CA and high short-circuit current density for SM-Reh, and delivers a record power conversion efficiency (PCE) of 16.34% with a high FF of 77.5%, which is much higher than 15.41% for SM-CA and 14.76% for SM-Reh. However, SM-CA-ID and SM-ID give the lower PCE of 8.20% and 2.76%. Characterization results suggest that the π-π interaction mainly dictates the packing morphology of blend films instead of dipole effect or crystallinity. Mono-substitution of Reh facilitates the molecular demixing appropriately but keeps the characteristic of the fine bicontinuous network of SM-CA:N3. SM-CA-Reh:N3 shows more efficient exciton extraction, higher hole transport, and better miscibility. These results well explain the merits integration and improved photovoltaic performance.