Localized surface plasmon resonance (LSPR) of doped Si nanocrystals (NCs) is critical to the development of Si-based plasmonics. We now experimentally show that LSPR can be obtained from both B- and P-doped Si NCs in the mid-infrared region. Both experiments and calculations demonstrate that the Drude model can be used to describe the LSPR of Si NCs if the dielectric screening and carrier effective mass of Si NCs are considered. When the doping levels of B and P are similar, the LSPR energy of B-doped Si NCs is higher than that of P-doped Si NCs because B is more efficiently activated to produce free carriers than P in Si NCs. We find that the plasmonic coupling between Si NCs is effectively blocked by oxide at the NC surface. The LSPR quality factors of B- and P-doped Si NCs approach those of traditional noble metal NCs. We demonstrate that LSPR is an effective means to gain physical insights on the electronic properties of doped Si NCs. The current work on the model semiconductor NCs, i.e., Si NCs has important implication for the physical understanding and practical use of semiconductor NC plasmonics.

Excess lead iodide (PbI2), as a defect passivation material in perovskite films, contributes to the longer carrier lifetime and reduced halide vacancies for high‐efficiency perovskite solar cells. However, the random distribution of excess PbI2 also leads to accelerated degradation of the perovskite layer. Inspired by nanocrystal synthesis, here, a universal ligand‐modulation technology is developed to modulate the shape and distribution of excess PbI2 in perovskite films. By adding certain ligands, perovskite films with vertically distributed PbI2 nanosheets between the grain boundaries are successfully achieved, which reduces the nonradiative recombination and trap density of the perovskite layer. Thus, the power conversion efficiency of the modulated device increases from 20% to 22% compared to the control device. In addition, benefiting from the vertical distribution of excess PbI2 and the hydrophobic nature of the surface ligands, the modulated devices exhibit much longer stability, retaining 72% of their initial efficiency after 360 h constant illumination under maximum power point tracking measurement.

Hole transport layers (HTLs) play a crucial role in the efficiency and stability of perovskite solar cells (PSCs). The most efficient PSCs based on spiro-OMeTAD (Spiro) generally have stability problems. Here, NiO x /Spiro HTL has been designed and implemented by combining the advantages of these two films. The results indicated that a device based on a NiO x /Spiro HTL has faster hole extraction ability and better energy alignment than that of a pure Spiro device, thus improving the PCE from 19.8 to 21.66%. Compared with the 60% initial efficiency of Spiro-based devices, the NiO x /Spiro bilayer devices have higher stability and maintain 90% initial efficiency over 1200 h. In this work, NiO x is applied to perovskite devices with N−I−P configuration, which provides a possible mitigation strategy to reduce the V OC deficit for efficient and stable devices.

The doping of semiconductor nanocrystals (NCs), which is vital for the optimization of NC-based devices, remains a significant challenge. While gas-phase plasma approaches have been successful in incorporating dopant atoms into NCs, little is known about their electronic activation. Here, we investigate the electronic properties of doped silicon NC thin films cast from solution by field effect transistor analysis. We find that, analogous to bulk silicon, boron and phosphorus electronically dope Si NC thin films; however, the dopant activation efficiency is only ∼10(-2)-10(-4). We also show that surface doping of Si NCs is an effective way to alter the carrier concentrations in Si NC films.

There appears to be a controversy on whether remnant PbI 2 is beneficial to the performance of perovskite solar cells (PSCs). We have shown that PSCs with residual PbI 2 deposited by one-step antisolvent solution and two-step evaporationsolution method both have shown better performance than those without excess PbI 2 . X-ray diffraction with diverse X-ray incident angles combined with scanning electron microscopy and secondary-ion mass spectrometry is employed to identify the position of remnant PbI 2 . It reveals that residual PbI 2 is located at grain boundaries near the perovskite/hole-transporting layer interface area for the one-step antisolvent solution method, and the two-step evaporation-solution method situates the excess PbI 2 at grain boundaries and the electron transport layer/perovskite interface. The cell performance implies that grain boundary passivation is beneficial for promoting short-circuit current density, while interface passivation is more favorable to enhance open-circuit voltage and fill factor. The revealed passivation process indicates a deep understanding of remnant PbI 2 and contributes to the development of PSCs.