A new organic small molecule, DRTB-T, that incorporates a two-dimensional trialkylthienyl-substituted benzodithiophene core building block was designed and synthesized. DRTB-T has a band gap (E) of 2.0 eV with a low-lying highest occupied molecular orbital (HOMO) level of -5.51 eV. Nonfullerene small-molecule solar cells consisting of DRTB-T and a nonfullerene acceptor (IC-C6IDT-IC) were constructed, and the morphology of the active layer was fine-tuned by solvent vapor annealing (SVA). The device showed a record 9.08% power conversion efficiency (PCE) with a high open-circuit voltage (V = 0.98 V). This is the highest PCE for a nonfullerene small-molecule organic solar cell (NFSM-OSC) reported to date. Our notable results demonstrate that the molecular design of a wide band gap (WBG) donor to create a well-matched donor-acceptor pair with a low band gap (LBG) nonfullerene small-molecule acceptor, as well as subtle morphological control, provides great potential to realize high-performance NFSM-OSCs.

Organic-inorganic hybrid perovskite solar cells represent an exceptional candidate for nextgeneration photovoltaic technology. However, the presence of surface defects in perovskite crystals limits the performance as well as the stability of perovskite solar cells. We have employed a series of carbazole and benzothiadiazole (BT) based donor-acceptor copolymers, which have different lengths of alkoxy side-chains grafted on the BT unit, as the dopant-free hole transport materials (HTMs) for perovskite solar cells. We demonstrate that although these side-chains can reduce the  stacking structural order of these copolymers to affect the hole transport properties, the methoxy unit introduces a desired defect passivation effect. Compared to the Spiro-OMeTAD-based device, the copolymer with methoxy side-chains on the BT unit (namely PCDTBT1) as the HTM achieved superior power conversion efficiency and stability due to efficient hole transport and the suppression of trap-induced degradation, whilst the copolymer with octyloxy side-chains on the BT unit (namely PCDTBT8) as the HTM lead to poor performance and stability.

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In bulk-heterojunction organic solar cells (BHJ-OSCs), exciton dissociation and charge transport are highly sensitive to the molecular packing pattern and phase separation morphology in blend films. Efficient photovoltaic small molecules (SMs) typically possess an acceptor−donor−acceptor structure that causes intrinsic anisotropy, limiting the control over molecular packing because of the lack of an effective method for modulating molecular orientation. In this report, we design a group of model compounds, named DRTB-T-CX (X = 2, 4, 6, and 8), to demonstrate that adjusting the length of the end alkyl chain can be used to modify the molecular orientation. A top-performance power conversion efficiency (PCE) of up to 11.24% is achieved with a DRTB-T-C4/ IT-4F-based device, which is the best performance reported for a state-of-the-art nonfullerene SM organic solar cell (NFSM-OSC).

High performance n–i–p type planar heterojunction PSCs with eliminated hysteresis and stabilized power output over 20% via compositional and surface modifications to a low-temperature-processed TiO2 electron-transport layer (ETL) is reported.

We model the strategic interaction between fundamental investors and “back-runners,” whose only information is about the past order flow of fundamental investors. Back-runners partly infer fundamental investors’ information from their order flow and exploit it in subsequent trading. Fundamental investors counteract back-runners by randomizing their orders, unless back-runners’ signals are too imprecise. Surprisingly, a higher accuracy of back-runners’ order flow information can harm back-runners and benefit fundamental investors. As an application of the model, the common practice of payment for (retail) order flow reveals information about institutional order flow and enables back-runners to earn large profits. (JEL G14, G18)

The π-conjugated organic small molecule 4,4′-cyclohexylidenebis[N,N-bis(4methylphenyl) benzenamine] (TAPC) has been explored as an efficient hole transport material to replace poly(3,4-ethylenedio-xythiophene):poly(styrenesulfonate) (PEDOT:PSS) in the preparation of p-i-n type CH 3 NH 3 PbI 3 perovskite solar cells. Smooth, uniform, and hydrophobic TAPC hole transport layers can be facilely deposited through solution casting without the need for any dopants. The power conversion efficiency of perovskite solar cells shows very weak TAPC layer thickness dependence across the range from 5 to 90 nm. Thermal annealing enables improved hole conductivity and efficient charge transport through an increase in TAPC crystallinity. The perovskite photoactive layer cast onto thermally annealed TAPC displays large grains and low residual PbI 2 , leading to a high charge recombination resistance. After optimization, a stabilized power conversion efficiency of 18.80% is achieved with marginal hysteresis, much higher than the value of 12.90% achieved using PEDOT:PSS. The TAPC-based devices also demonstrate superior stability compared with the PEDOT:PSS-based devices when stored in ambient circumstances, with a relatively high humidity ranging from 50 to 85%.

We review recent progress in the development of organometal halide perovskite solar cells. We discuss different compounds used to construct perovskite photoactive layers, as well as the optoelectronic properties of this system. The factors that affect the morphology of the perovskite active layer are explored, e.g. material composition, film deposition methods, casting solvent and various post-treatments. Different strategies are reviewed that have recently emerged to prepare high performing perovskite films, creating polycrystalline films having either large or small grain size. Devices that are constructed using meso-superstructured and planar architectures are summarized and the impact of the fabrication process on operational efficiency is discussed. Finally, important research challenges (hysteresis, thermal and moisture instability, mechanical flexibility, as well as the development of lead-free materials) in the development of perovskite solar cells are outlined and their potential solutions are discussed.