Finding effective molecular design strategies to optimize the active layer blend morphology is among the long-standing challenges in developing efficient allpolymer solar cells (all-PSCs). Here we show that new biselenophene/selenophenelinked naphthalene diimide random copolymer acceptors BSSx (x = 10, 20, 50) facilitate the achievement of high-performance all-PSCs without the use of any solution processing additive. Blends of BSS10 with donor polymer PBDB-T combined 10.1% power conversion efficiency with 97% internal quantum efficiency and 0.59 eV optical band gap energy loss (E loss ). BSS10-and BSS20-based devices have the best combination of high external quantum efficiency (>85%) and small E loss (<0.6 eV) among all-PSCs yet reported. The results demonstrate that the blend morphology, charge carrier mobilities, and photovoltaic properties of all-PSCs could be rationally optimized by means of a synthetic variablethe random copolymer composition.

Understanding the influence of polymer molecular weight on the morphology, photophysics, and photovoltaic properties of polymer solar cells is central to further advances in the design, processing, performance and optimization...

We study the organic electrochemical transistor (OECT) performance of the ladder polymer poly-(benzimidazobenzophenanthroline) (BBL) in an attempt to better understand how an apparently hydrophobic side-chain-free polymer is able to operate as an OECT with favorable redox kinetics in an aqueous environment. We examine two BBLs of different molecular masses from different sources. Regardless of molecular mass, both BBLs show significant film swelling during the initial reduction step. By combining electrochemical quartz crystal microbalance gravimetry, in-operando atomic force microscopy, and both ex-situ and in-operando grazing incidence wideangle X-ray scattering (GIWAXS), we provide a detailed structural picture of the electrochemical charge injection process in BBL in the absence of any hydrophilic side-chains. Compared with ex-situ measurements, in-operando GIWAXS shows both more swelling upon electrochemical doping than has previously been recognized and less contraction upon dedoping. The data show that BBL films undergo an irreversible hydration driven by the initial electrochemical doping cycle with significant water retention and lamellar expansion that persists across subsequent oxidation/ reduction cycles. This swelling creates a hydrophilic environment that facilitates the subsequent fast hydrated ion transport in the absence of the hydrophilic side-chains used in many other polymer systems. Due to its rigid ladder backbone and absence of hydrophilic side-chains, the primary BBL water uptake does not significantly degrade the crystalline order, and the original dehydrated, unswelled state can be recovered after drying. The combination of doping induced hydrophilicity and robust crystalline order leads to efficient ionic transport and good stability.