To achieve a conjugated drug delivery system with high drug loading but minimal long-term side effects, a degradable brush polymer-drug conjugate (BPDC) was synthesized through azide-alkyne click reaction of acetylene-functionalized polylactide (PLA) with azide-functionalized paclitaxel (PTXL) and poly(ethylene glycol) (PEG). Well-controlled structures of the resulting BPDC and its precursors were verified by (1)H NMR and gel permeation chromatography (GPC) characterizations. With nearly quantitative click efficiency, drug loading amount of the BPDC reached 23.2 wt %. Both dynamic light scattering (DLS) analysis and transmission electron microscopy (TEM) imaging indicated that the BPDC had a nanoscopic size around 10-30 nm. The significant hydrolytic degradability of the PLA backbone of the BPDC was confirmed by GPC analysis of its incubated solution. Drug release study showed that PTXL moieties can be released through the cleavage of the hydrolyzable conjugation linkage in pH 7.4 at 37 °C, with 50% release in about 22 h. As illustrated by cytotoxicity study, while the polymeric scaffold of the BPDC is nontoxic, the BPDC exhibited higher therapeutic efficacy toward MCF-7 cancer cells than free PTXL at 0.1 and 1 μg/mL. Using Nile red as encapsulated fluorescence probe, cell uptake study showed effective internalization of the BPDC into the cells.

All‐conjugated block copolymers bring together hole‐ and electron‐conductive polymers and can be used as the active layer of solution‐processed photovoltaic devices, but it remains unclear how molecular structure, morphology, and electronic properties influence performance. Here, the role of the chemical linker is investigated through analysis of two donor–linker–acceptor block copolymers that differ in the chemistry of the linking group. Device studies show that power conversion efficiencies differ by a factor of 40 between the two polymers, and ultrafast transient absorption measurements reveal charge separation only in block copolymers that contain a wide bandgap monomer at the donor–acceptor interface. Optical measurements reveal the formation of a low‐energy excited state when donor and acceptor blocks are directly linked without this wide bandgap monomer. For both samples studied, it is found that the rate of charge recombination in these systems is faster than in poly­mer–polymer and polymer–fullerene blends. This work demonstrates that the linking group chemistry influences charge separation in all‐conjugated block copolymer systems, and further improvement of photovoltaic performance may be possible through optimization of the linking group. These results also suggest that all‐conjugated block copolymers can be used as model systems for the donor–acceptor interface in bulk heterojunction blends.

All-conjugated block copolymers may be an effective route to self-assembled photovoltaic devices, but we lack basic information on the relationship between molecular characteristics and photovoltaic performance. Here, we synthesize a library of poly(3-hexylthiophene) (P3HT) block poly((9,9-dialkylfluorene)-2,7-diyl-alt-[4,7-bis(alkylthiophen-5-yl)-2,1,3-benzothiadiazole]-2′,2″-diyl) (PFTBT) donorblock-acceptor all-conjugated block copolymers and carry out a comprehensive study of processing conditions, crystallinity, domain sizes, and side-chain structure on photovoltaic device performance. We find that all block copolymers studied exhibit an out-of-plane crystal orientation after deposition, and on thermal annealing at high temperatures the crystal orientation flips to an in-plane orientation. By varying processing conditions on polymer photovoltaic devices, we show that the crystal orientation has only a modest effect (15−20%) on photovoltaic performance. The addition of side chains to the PFTBT block is found to decrease photovoltaic power conversion efficiencies by at least an order of magnitude. Through grazing-incidence X-ray measurements we find that the addition of side chains to the PFTBT acceptor block results in weak segregation and small (<10 nm) block copolymer self-assembled donor and acceptor domains. This work is the most comprehensive to date on all-conjugated block copolymer systems and suggests that photovoltaic performance of block copolymers depends strongly on the miscibility of donor and acceptor blocks, which impacts donor and acceptor domain sizes and purity. Strategies for improving the device performance of block copolymer photovoltaics should seek to increase segregation between donor and acceptor polymer domains.

Bulk heterojunction organic photovoltaic (OPV) devices are multilayer organic devices that can be fabricated using low-cost and scalable solution processing methods, but current devices exhibit poor mechanical stability and degrade under deformation due to cracking and delamination. Recent approaches to improve mechanical durability involve modifying the side-chain or main-chain structures of conjugated polymers in the active layer, but in general it is difficult to simultaneously optimize electronic properties, morphology, and mechanical stability. Here, we present a general approach to improve the mechanical stability of bulk heterojunction active layers through incorporation of an internal elastic network. Network-stabilized bulk heterojunction OPVs are prepared using reactive small molecular additives that are rapidly cross-linked through thiol−ene coupling after processing the active layer. Thiol−ene reactions catalyzed by a base or initiated through short exposure to UV light produce insoluble, elastic thiol−ene networks in the active layer. We show through a combination of crack onset strain measurements, morphological analysis, and OPV device testing that network-stabilized OPVs with up to 20% thiol−ene network exhibit improved deformability with no loss in PCE, and we implement networkstabilized bulk heterojunction OPVs to produce stretchable photovoltaic devices. This work represents a simple approach for improving the mechanical durability of bulk heterojunction OPVs.

The bicontinuous microemulsion (BμE) phase is an equilibrium morphology characterized by cocontinuous domains, high interfacial areas, and nanoscale domain dimensions. These characteristics make the BμE potentially suitable for use in organic photovoltaic applications. Here, we use a combination of simulations and experiments to investigate the equilibrium morphologies formed by a ternary blend of conjugated polymer, all-conjugated diblock copolymer, and fullerene derivative PCBM. Using coarse-grained simulations, we identify the blend compositions that are most likely to result in donor/acceptor morphologies resembling the BμE. Experimentally, we probe these compositions through transmission electron microscopy and grazing-incidence X-ray scattering measurements. We demonstrate that all-conjugated block copolymer additives can be used to produce thermally stable, cocontinuous donor/acceptor morphologies at higher additive contents and longer annealing times than previously reported. These results demonstrate that conjugated BCP compatibilizers can be used as a means to achieve equilibrium, cocontinuous morphologies in donor/acceptor blends.O rganic solar cells (OSCs) based on the conjugated polymer/PCBM blend boast the shortest expected energy payback time among various photovoltaic technologies. 1 However, two of the primary challenges still limiting the marketability of these devices are (i) the lower device efficiency of the OSC relative to the more conventional silicon-based solar cell and (ii) the long-term thermal instability of the device active layer. 2 Indeed, high performance organic solar cells are typically based on kinetically determined morphologies that degrade upon thermal annealing. In contrast, the achievement of equilibrium donor/acceptor morphologies with the characteristics known to yield high device performance could provide an effective form of solar energy harvesting that remains stable over time.The bicontinuous microemulsion (BμE) 3−5 is a well-known equilibrium morphology characterized by cocontinuous domains, high interfacial areas, and nanoscale domain dimensions. These characteristics make the BμE potentially suitable for use as an "ideal" device active layer in organic photovoltaic applications. In the context of polymeric systems, the BμE is often achieved by the addition of a diblock copolymer compatibilizer (AB) to a blend of two immiscible homopolymers (A and B). 4 Previous studies have demonstrated the rational design of BμEs using a variety of flexible polymeric materials. 6−8 Unfortunately, these f lexible polymer materials are typically inappropriate for use in OSC active layers. However, recent simulations by Kipp et al. demonstrated that diblock copolymer compatibilizers can also be used as an additive in semif lexible polymer/solvent blends to achieve BμE phases (the authors studied this system as a model for the conjugated polymer/PCBM system often used in OSCs). 9,10 Whether morphologies like those resulting from the simulations are accessible to the experiments remain...