The principal criteria for a polymer-based electron-transport layer (ETL) for use in polymer light-emitting diodes (PLEDs) are the following: 1) the lowest unoccupied molecular orbital (LUMO) of the ETL must be at an energy close to, or even within the p*-band of the emissive semiconducting polymer, and 2) the solvent used for casting the electron-injection material must not dissolve the underlying emissive polymer. Although a few attempts to satisfy these criteria have been reported, [1,2] none have succeeded in avoiding interfacial mixing in multilayer PLEDs.In this contribution, we report the synthesis of the cationic, conjugated alternating copolymer, poly{ [9,9-bis(6¢-(N,N,N- were added to the reaction mixture, followed by 5 mL water. The reaction was degassed and refluxed for 48 h under Ar. The reaction mixture was then extracted with chloroform and washed with water and brine. Drying on anhydrous magnesium sulfate, filtration, and evaporation of the solvent gave the crude compound. Precipitating three times from acetone gave the desired polymer 3 (0.231 g, 55 %). Polymer 3 (0.125 g, 0.195 mmol) was dissolved in 10 mL tetrahydrofuran (THF) and stirred at room temperature, after which 1 mL methyl iodide was added to the reaction. Within 2 min a precipitate formed. After stirring for 30 min, 5 mL water was added to the reaction mixture. Stirring was continued at room temperature for 48 h. The solvent was evaporated to dryness and acetone was added to the flask. The acetone was decanted carefully and this was repeated three times. The precipitates were filtered and dried to obtain the desired polymer, PFON + (CH 3 ) 3 I ± ±PBD (0.155 g, 86 %).Figure 1 compares the current density, J, and brightness, L, (versus voltage) characteristics of devices made using poly(9,9-dioctyfluorenyl-2,7-diyl) (PFO), with and without COMMUNICATIONS 274

at pH 9.0, 64 %. Similarly, 0.1 M UMP increases the size of a typical polymer film at pH 7.0 by 28 %, but at pH 11.0 by 140 %. Solely pH-dependent macroscopic changes have been described earlier with natural polymers such as chitosan [6] and gelatin derivatives, [7] and they are due to repulsions of charged loci within and between the polymer chains.[8] The significantly increased macroscopic dimension change by effector uptake at higher pH observed here can be understood by the presence of a less tight polymer network in the more deprotonated state, which, due to its higher flexibility, can better accommodate the added guest compounds. The observed cooperativity creates new possibilities for designing macroscopic supramolecular systems, which can be fine-tuned to respond only to a given combination of different effector compounds at distinct concentrations. Such systems can be of interest for actuators including artificial muscles, vessels, or implants, for self-regulating valves in process control, for sensors, and other related applications. Possible applications for drug release or uptake can take advantage of the necessary presence of a certain combination of effectors. The new self-controlled logic gates could directly communicate with the outside world like a natural organ. Obviously, supramolecular chemistry within suitably functionalized polymers extends significantly over that possible with traditional host± guest complexes in solution, as evidenced by the observed strong cooperativity based on relatively simple binding units. It should be emphasized that the sensitivity of such systems can be greatly enhanced by changes in volume and capacity of the polymer particles, and that manifold known recognition sites can be incorporated into such intelligent materials.

A major limit for planar perovskite solar cells is the trap‐mediated hysteresis and instability, due to the defective metal oxide interface with the perovskite layer. Passivation engineering with fullerenes has been identified as an effective approach to modify this interface. The rational design of fullerene molecules with exceptional electrical properties and versatile chemical moieties for targeted defect passivation is therefore highly demanded. In this work, novel fulleropyrrolidine (NMBF‐X, XH or Cl) monomers and dimers are synthesized and incorporated between metal oxides (i.e. TiO2, SnO2) and perovskites (i.e. MAPbI3 and (FAPbI3)x(MAPbBr3)1‐x). The fullerene dimers provide superior stability and efficiency improvements compared to the corresponding monomers, with chlorinated fullerene dimers being most effective at coordinating with both metal oxides and perovskite via the chlorine terminals. The non‐encapsulated planar device delivers a maximum power conversion efficiency of 22.3% without any hysteresis, while maintaining over 98% of initial efficiency after ambient storage for 1000 h, and exhibiting an order of magnitude improvement of the T80 lifetime.

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