We examine the impact of social capital on audit fees. We find that firms headquartered in U.S. counties with high social capital pay lower audit fees. Social capital measures the level of mutual trust in a region. Our results suggest that auditors judge the trustworthiness of their clients based on where the firm is headquartered and charge a premium when they trust the firm less. The basis of our results is the examination of more than 28,000 audit fees for more than 5,000 firms spanning the period of 2000 to 2009. The results are robust to controlling for a large number of firm-level and county-level characteristics. JEL Classifications: M42; M14.

A highly efficient fullerene-free polymer solar cell (PSC) based on PDCBT, a polythiophene derivative substituted with alkoxycarbonyl, achieves an impressive power conversion efficiency of 10.16%, which is the best result in PSCs based on polythiophene derivatives to date. In comparison with a poly(3-hexylthiophene):ITIC-based device, the photovoltaic and morphological properties of the PDCBT:ITIC-based device are carefully investigated and interpreted.

Monodisperse, ultrasmall (<5 nm) Cu(2-x)S nanodots (u-Cu(2-x)S NDs) with significantly strong near-infrared absorption and conversion are successfully demonstrated for effective deep-tissue photoacoustic imaging-guided photothermal therapy both in vitro and in vivo. Owing to ultrasmall nanoparticle size and high water dispersibility as well as long stability, such nanodots possess a prolonged circulation in blood and good passive accumulation within tumors through the enhanced permeability and retention effect. These u-Cu(2-x)S NDs have negligible side effects to both blood and normal tissues according to in vivo toxicity evaluations for up to 3 months, showing excellent hemo/histocompatibility. Furthermore, these u-Cu(2-x)S NDs can be thoroughly cleared through feces and urine within 5 days, showing high biosafety for further potential clinical translation. This novel photoacoustic imaging-guided photothermal therapy based on u-Cu(2-x)S NDs composed of a single component shows great prospects as a multifunctional nanoplatform with integration and multifunction for cancer diagnosis and therapy.

A robust superhydrophobic surface with high performances of photothermal-conversion and light-driven motion has been fabricated by integrating with hydrophobic two-dimensional MXenes.

Using an environmentally friendly solvent, N-methyl-2-pyrrolidone, a polymer with benzodithiophene (BDT) and thieno[3,4-b]thiophene (TT) monomers and triethylene glycol monoether (TEG) side chains, PBDTTT-TEG, can be processed into an active layer for a polymer solar cell (PSC). Combined with phenyl-C 71-butyric acid methyl ester (PC 71 BM) as the acceptor, the resulting PSC has a power conversion efficiency (PCE) of 5.23%. This is the first example of an efficient polymer solar cell fabricated from a non-aromatic and nonchlorinated solvent.

Tandem organic solar cells (TOSCs), which integrate multiple organic photovoltaic layers with complementary absorption in series, have been proved to be a strong contender in organic photovoltaic depending on their advantages in harvesting a greater part of the solar spectrum and more efficient photon utilization than traditional single-junction organic solar cells. However, simultaneously improving open circuit voltage (V ) and short current density (J ) is a still particularly tricky issue for highly efficient TOSCs. In this work, by employing the low-bandgap nonfullerene acceptor, IEICO, into the rear cell to extend absorption, and meanwhile introducing PBDD4T-2F into the front cell for improving V , an impressive efficiency of 12.8% has been achieved in well-designed TOSC. This result is also one of the highest efficiencies reported in state-of-the-art organic solar cells.

MXenes, a new class of two‐dimensional (2D) nanomaterials, have shown enormous potential for biological applications. Notably, the development of 2D MXenes in nanomedicine is still in its infancy. Herein, a distinct W1.33C i‐MXene with multiple theranostic functionalities, fast biodegradation, and satisfactory biocompatibility is explored. By designing a parent bulk laminate in‐plane ordered (W2/3Y1/3)2AlC ceramic and optionally etching aluminum (Al) and yttrium (Y) elements, 2D W1.33C i‐MXene nanosheets with ordered divacancies are efficiently fabricated. Especially, theoretical simulations reveal that W1.33C i‐MXene possesses a strong predominance of near‐infrared (NIR) absorbance. The constructed ultrathin W1.33C nanosheets feature excellent photothermal‐conversion effectiveness (32.5% at NIR I and 49.3% at NIR II) with desirable biocompatibility and fast degradation in normal tissue rather than in tumor tissue. Importantly, the multimodal‐imaging properties and photothermal‐ablation performance of W1.33C‐BSA nanosheets are systematically revealed and demonstrated both in vitro and in vivo. The underlying mechanism and regulation factors for the W1.33C‐BSA nanosheets‐induced hyperthermia ablation are also revealed by transcriptome and proteome sequencing. This work offers a paradigm that i‐MXenes achieve the tailoring biomedical applications through composition and structure design on the atomic scale.

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