In n–i–p-type conventional perovskite solar cells (PSCs) using a doped 2,2′,7,7′-tetrakis (N,N′-di-p-methoxyphenylamine)-9,9′-spirofluorene (spiro-OMeTAD) hole transport layer (HTL), the issues of reproducibility and stability are closely associated with the redox-inactive additives lithium bis­(trifluoromethanesulfonyl)­imide (Li-TFSI) and 4-tert-butylpyridine (tBP). Instead of these additives, copper­(II) di­[bis­(trifluoromethylsulfonyl)­imide] (Cu­(TFSI)2) is demonstrated as a direct and efficient p-dopant for spiro-OMeTAD. With the adoption of the technologically relevant coevaporation technique, highly uniform, pinhole-free doped HTLs are achieved with controlled amounts of Cu­(TFSI)2 and are spectroscopically and electrically characterized. Using these highly conducting doped HTLs, CH3NH3PbI3-based planar PSCs are realized, which exhibit high photoconversion efficiency (>13% with merely 4 mol % dopant) and excellent reproducibility. Also, by taking advantage of the coevaporation technique, the Cu­(TFSI)2-doped HTL thickness impact on PSCs is investigated. It is observed that devices with even the thinnest (40 nm) HTL perform very similarly to the ones with a 100 nm thick HTL, which opens up cost-effective preparation strategies. Moreover, a remarkable storage stability over 218 days is observed for devices with a coevaporated Cu­(TFSI)2-doped HTL, suggesting that this approach of controlled direct doping is a viable alternative to the existing arbitrarily p-doped HTL in perovskite solar cells.

The synthesis of two new conjugated polymers based on the relatively under‐exploited monomer, 5,8‐dibromo‐2‐[5‐(2‐hexyldecyl)‐2‐thienyl]‐1H‐dithieno[3,2‐e:2′,3′‐g]benzimidazole (dithienobenzimidazole, DTBI), and either 4,7‐bis[4‐hexyl‐5‐(trimethylstannyl)‐2‐thienyl]‐2,1,3‐benzothiadiazole (BTD) or 2,6‐bis(trimethylstannyl)‐4,8‐bis(5‐(2‐ethylhexyl) thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene (BDT) is described. The polymers were synthesized via Stille polycondensation and characterized by traditional methods (1H NMR, gel‐permeation chromatography, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry, thermal gravimetric analysis, differential scanning calorimetry, ultraviolet–visible spectroscopy, photoluminescence, and cyclic voltammetry). Prior to their synthesis, trimer structures were modeled by DFT calculations facilitating a further understanding of the systems' electronic and geometric structure. Polymers were titrated with acid and base to take advantage of their amphiprotic imidazole moiety and their optical response monitored with ultraviolet–visible spectroscopy. Finally, pristine polymer thin‐films were treated with acid and base to evaluate (de)protonation's effect on system electronics, but thin‐film degradation was encountered. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 60–69

The fourth dimension in 4D printing comprises the ability of materials to recover their shape with time by utilizing 3D printing in combination with shape memory polymers. The focus of this work is on 3D printing of physically crosslinked thermoplastic polymers, which allow a reversible transformation from a temporary to an original shape by an external stimulus temperature, thus realize 4D printing. In this context, (AB)n segmented copolyetherimides consisting of perylene and poly(ethylene glycol) (PEG) segments are synthesized and characterized regarding their thermal and rheological properties in view of 3D printing. The perylene imide segments act as reversible physical crosslinks which disassemble between 100 and 200 °C. The PEG segments exhibit a low melting temperature around 40 to 60 °C and are semi‐crystalline at room temperature. The results show that this type of (AB)n segmented copolyetherimide combines reliable 3D printing performance, which is indicated by low warp deformation and excellent interlayer bonding. With a blend of two copolymers, it is able to realize 4D printing.