• Energy Research

A series of copolymers of cyclopentadiene and DPP unit with different side chains were synthesized. The copolymer with longer linear alkyl spacer and shorter branches exhibited superior performance and the highest mobility up to 2.1 cm2 V−1 s−1.

AbstractCompared to fullerene based electron acceptors, n-type organic semiconductors, so-called non-fullerene acceptors (NFAs), possess some distinct advantages, such as readily tuning of optical absorption and electronic energy levels, strong absorption in the visible region and good morphological stability for flexible electronic devices. The design and synthesis of new NFAs have enabled the power conversion efficiencies (PCEs) of organic photovoltaic (OPV) devices to increase to around 19%. This review summarises the important breakthroughs that have contributed to this progress, focusing on three classes of NFAs, i.e. perylene diimide (PDI), diketopyrrolopyrrole (DPP) and acceptor–donor–acceptor (A-D-A) based NFAs. Specifically, the PCEs of PDI, DPP, and A-D-A series based non-fullerene OPVs have been reported up to 11%, 13% and 19%, respectively. Structure–property relationships of representative NFAs and their impact on OPV performances are discussed. Finally, we consider the remaining challenges and promising directions for achieving high-performing NFAs.

Organic photodetectors have great potential in near-infrared applications. Here we develop new non-fullerene acceptors with detection above 800 nm and demonstrated large area devices with record performances.

A series of four n-type semiconducting copolymers containing a 2,1,3-benzothiadiazole (BT) based acceptor annulated with a 2-(1,3-dithiol-2-ylidene)malonitrile group are synthesized and their optoelectronic properties investigated.

Two benzothiadiazole derivatives annulated with 2-(1,3-dithiol-2-ylidene)malonitrile in the 4,5-position were prepared by a one-step procedure, and investigated as end-groups in non-fullerene acceptors for indoor photovoltaic applications.

AbstractTwo fully non‐fused small‐molecule acceptors BTIC‐1 and BTIC‐2 are reported for application in near‐infrared organic photodetectors (NIR OPDs). Both acceptors contain the same conjugated backbone but differing sidechain regiochemistry, affording significant differences in their optical properties. The head‐to‐head arrangement of BTIC‐2 results in a reduction of optical band gap of 0.17 eV compared to BTIC‐1, which contains a head‐to‐tail arrangement, with absorption spanning the visible and near‐IR regions up to 900 nm. These differences are rationalized on the basis of non‐covalent intramolecular interactions facilitating a more co‐planar conformation for BTIC‐2. OPDs based on PM6:BTIC‐2 deliver a low dark current density of 2.4 × 10−7 A cm−2, leading to a superior specific detectivity of 1.7 × 1011 Jones at 828 nm at ‐2 V. The optimized device exhibits an ultrafast photo response of 2.6 µs and a high ‐3 dB cut‐off frequency of 130 kHz. This work demonstrates that fully non‐fused small‐molecule acceptors offer competitive device performance for NIR OPDs compared to fused‐ring electron acceptors, but with reduced synthetic complexity. Furthermore, the study presents an efficient strategy to enhance device performance by varying conformational locks.

We present a new framework to study organic photovoltaic devices in which a model that integrates device physics with excited state dynamics is applied to explain transient and steady-state spectroscopic and optoelectronic measurements.

Bisthienoazepinedione (BTA) has been reported for constructing high-performing p-type conjugated polymers in organic electronics, but the ring extended version of BTA is not well explored. In this work, we report a new synthesis of a key building block to the ring expanded electron-deficient pentacyclic azepinedione (BTTA). Three copolymers of BTAA with benzodithiophene substituted by different side chains are prepared. These polymers exhibit similar energy levels and optical absorption in solution and solid state, while significant differences are revealed in their film morphologies and behavior in transistor and photovoltaic devices. The best-performing polymers in transistor devices contained alkylthienyl side chains on the BDT unit (pBDT-BTTA-2 and pBDT-BTTA-3) and demonstrated maximum saturation hole mobilities of 0.027 and 0.017 cm2 V-1 s-1. Blends of these polymers with PC71BM exhibited a best photovoltaic efficiency of 6.78% for pBDT-BTTA-3-based devices. Changing to a low band gap non-fullerene acceptor (BTP-eC9) resulted in improved efficiency of up to 13.5%. Our results are among the best device performances for BTA and BTTA-based p-type polymers and highlight the versatile applications of this electron-deficient BTTA unit.