Highly oriented films of an electron accepting polymer semiconductor, poly{[N,N'-bis(2-octyldodecyl)-1,4,5,8-naphthalenedicarboximide-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (PNDI2OD-T2), are obtained by two different methods, namely directional epitaxial crystallization (DEC) on 1,3,5-trichlorobenzene (TCB) and epitaxy on friction transferred poly(tetrafluoroethylene) (PTFE) substrates. Two distinct polymorphs with unprecedented intrachain resolution are identified by high-resolution transmission electron microscopy (HR-TEM). Form I is obtained by DEC on TCB, whereas highly oriented films of form II are obtained on PTFE substrates after melting at T = 300 °C and cooling at 0.5 K/min. In form I, both electron diffraction and HR-TEM indicate a segregated stacking of bithiophene (T2) and naphthalene diimide (NDI) units forming separate columns. In form II, a ∼c/2 shift between successive π-stacked chains leads to mixed π-overlaps of T2 and NDI. Form I can be transformed into form II by annealing at T > 250 °C. The different π-stacking of NDI and T2 in the two polymorphs have characteristic signatures in the UV-vis spectra, especially in the charge transfer band around 750 nm which is also observed in spin-coated films.

The power conversion efficiency of inorganic–organic hybrid lead halide perovskite solar cells (PSCs) is approaching that of those made from single crystalline silicon; however, they still experience problems such as hysteresis and photo/electrical‐field‐induced degradation. Evidences consistently show that ionic migration is critical for these detrimental behaviors, but direct in‐situ studies are still lacking to elucidate the respective kinetics. Three different PSCs incorporating phenyl‐C61‐butyric acid methyl ester (PCBM) and a polymerized form (PPCBM) is fabricated to clarify the function of fullerenes towards ionic migration in perovskites: 1) single perovskite layer, 2) perovskite/PCBM bilayer, 3) perovskite/PPCBM bilayer, where the fullerene molecules are covalently linked to a polymer backbone impeding fullerene inter‐diffusion. By employing wide‐field photoluminescence imaging microscopy, the migration of iodine ions/vacancies under an external electrical field is studied. The polymerized PPCBM layer barely suppresses ionic migration, whereas PCBM readily does. Temperature‐dependent chronoamperometric measurements demonstrate the reduction of activation energy with the aid of PCBM and X‐ray photoemission spectroscopy (XPS) measurements show that PCBM molecules are viable to diffuse into the perovskite layer and passivate iodine related defects. This passivation significantly reduces iodine ions/vacancies, leading to a reduction of built‐in field modulation and interfacial barriers.

Well-soluble fullerene-grafted copolymers PPCBMs with high contents of pendant phenyl-C61-butyric acid methyl ester (PCBM) between 30 and 64 wt % are reported. Herein, the tailor-made precursor copolymers poly(4-methoxystyrene-stat-4-tert-butoxystyrene) obtained by reversible addition–fragmentation chain transfer (RAFT) polymerization are functionalized via an efficient polymer-analogous esterification. The synthesized acceptor copolymers retain the optical and electrochemical properties of the incorporated PCBM independent of their fullerene weight fraction. Their electron transport properties are studied by the space-charge limited current (SCLC) method. The maximum electron mobility μe of 1 × 10–4 cm2 V–1 s–1 is achieved for 37 wt % of incorporated PCBM. Below 50 wt % of PCBM, the acceptor polymers exhibit exceptional high charge carrier mobility compared to the corresponding blends of molecular PCBM and precursor copolymer. Detailed structural studies using AFM, TEM, and XRD are performed. We confirm amorphous morphology both in thin films and in bulk for the PPCBMs, which clearly indicates the absence of PCBM nanocrystals. Thus, an efficient charge carrier percolation is facilitated by the homogeneous distribution of PCBM in the copolymer. Additionally, the absence of nanocrystal formation was demonstrated during thermal annealing.

A series of tailor-made poly­(3-hexylthiophene)-block-PPCBM (P3HT-b-PPCBM) block copolymers incorporating P3HT as donor and a polystyrene with pendant fullerenes (PC61BM) as acceptor block (PPCBM) is presented. The grafting density of PC61BM was varied between 26 and 60 wt %. This has high impact on structure formation, molecular dynamics, and charge transport. It causes considerable increase in glass transition temperature (T g from 150 to 200 °C). The T g of the amorphous PPCBM block restricts the dynamics of structure evolution of the block copolymer resulting in an incomplete microphase separation, although structural studies revealed a donor–acceptor nanostructure of 30–40 nm in bulk and thin films. All block copolymers exhibit ambipolar charge transport in organic field-effect transistors. Further, the most densely grafted system showed 2 orders of magnitude higher electron mobility. Thus, the fullerene grafting density turned out as a key parameter in designing P3HT-b-PPCBM systems for tuning phase separation and charge transport.

A PC71BM-grafted donor–acceptor block copolymer with enhanced absorption showing a periodic nanostructure of 37 nm both in bulk and in thin films was synthesized by combining KCTP and CRP methods.