A new naphthalene diimide (NDI)‐based polymer with strong electron withdrawing dicyanothiophene (P(NDI2DT‐TTCN)) is developed as the electron transport layer (ETL) in place of the fullerene‐based ETL in inverted perovskite solar cells (Pero‐SCs). A combination of characterization techniques, including atomic force microscopy, scanning electron microscopy, grazing‐incidence wide‐angle X‐ray scattering, near‐edge X‐ray absorption fine‐structure spectroscopy, space‐charge‐limited current, electrochemical impedance spectroscopy, photoluminescence (PL), and time‐resolved PL decay, is used to demonstrate the interface phenomena between perovskite and P(NDI2DT‐TTCN) or [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM). It is found that P(NDI2DT‐TTCN) not only improves the electron extraction ability but also prevents ambient condition interference by forming a hydrophobic ETL surface. In addition, P(NDI2DT‐TTCN) has excellent mechanical stability compared to PCBM in flexible Pero‐SCs. With these improved functionalities, the performance of devices based on P(NDI2DT‐TTCN) significantly outperform those based on PCBM from 14.3 to 17.0%, which is the highest photovoltaic performance with negligible hysteresis in the field of polymeric ETLs.

Systematic side-chain engineering through adjustment of spacer groups in diketopyrrolopyrrole-thiophene vinylene thiophene (DPP-TVT) polymers reveals odd–even dependence of device performance.

We describe several strategies for the molecular design of high-efficiency blue fluorescent emitters. Asymmetric donor–acceptor (D–A) and symmetric A–D–A-type fluorescent emitters were designed with spiroacridine donors and diphenyltriazine acceptors. Substituting a toluene or xylene moiety for the phenyl group connecting the donor and acceptor and replacing the diphenylsilane group with a fluorene moiety resulted in a deeper blue emission without any losses in luminescence efficiency. On the basis of these substitutions, deep blue organic light emitting diodes (OLEDs) with Commission Internationale de L’Eclairage (CIE) coordinates of (0.149, 0.082) and an external quantum efficiency (EQE) of 7.7% were fabricated using a D–A-type emitter. Symmetrizing the D–A structure to an A–D–A structure increased the proportion of horizontally oriented emission dipoles in the organic film from 70 to 90%. OLEDs incorporating symmetric A–D–A-type emitters had EQEs as high as 8.5% due to increased outcoupling efficiencies and also showed deep blue emission with CIE coordinates of (0.142, 0.116). The molecular design strategies described herein can be applied to donor–acceptor-type fluorescent emitters for the fabrication of efficient deep blue OLEDs.

Photomultiplication‐type organic photodetectors (PM‐OPDs) with high external quantum efficiency (EQE) of over 100% are attracting increasing attention due to their potential importance in detecting weak incident light. Considering that the gain of PM‐OPD is determined by the ratio of carrier lifetime over carrier transit time, a systematic study on the effect of the end‐functionalization of a new extended aromatic fused‐ring non‐fullerene acceptor (NFA) on the carrier trap/transit time of the PM‐OPD. Photophysical analyses by means of ultraviolet‐visible absorption, ultraviolet photoelectron spectroscopy, and photoluminescence combined with structural analyses through grazing‐incidence wide‐angle X‐ray scattering show that fluorination of the NFA with the deepest lowest unoccupied molecular orbital level and non‐isotropic molecular ordering can yield the longest carrier lifetime. Furthermore, surface energy study show that fluorination of the NFA can also yield the most hydrophobic nature, which can allow the most efficient injection barrier thinning/lowering of the active layer/cathode interface under illumination due to the localized acceptor distribution toward cathode, maximizing the hole injection efficiency from cathode. As a result, an unprecedentedly high EQE of 156 000% is obtained from the optimized PM‐OPD. This work shows the importance of the molecular design of acceptor molecules in fabricating high‐performance PM‐OPDs.

A−D−A conjugated polymer, PTPD-TVT, containing thienopyrroledione and thiophene−vinylene−thiophene (TVT) units was synthesized as an electron donor for organic photovoltaic devices. It possesses a small bandgap and has excellent coplanarity and high hole mobility. To further enhance the interchain interactions between the polymer chains, a selenophene−vinylene−selenophene (SVS) unit was also introduced and copolymerized to form the PTPD-SVS polymer. Devices made from PTPD-TVT and PTPD-SVS have rather promising power conversion efficiencies (PCEs) of 4.87 and 5.74%, respectively. The higher PCE value for solar cells based on PTPD-SVS was attributed to an enhanced carrier mobility resulting from stronger interchain aggregation in the BHJ active layer. These results show that the incorporation of a vinylene unit in TPD-based polymers is an effective way to reduce the bandgap and thereby improve charge transport for efficient photovoltaic devices.