Surface-enhanced Raman scattering (SERS) spectra of 4-mercaptobenzoic acid (4-MBA) have been investigated on the surface of Cu₂O nanospheres. The SERS signals were believed to originate from the static chemical enhancement, resonant chemical enhancement and electromagnetic enhancement. The coupling between the adsorbates and the semiconductor, evidenced by the shift in absorption spectrum of modified Cu₂O and the enhancement of non-totally symmetric modes of the 4-MBA and 4-mercaptopyridine (4-MPY) molecules, were invoked to explain the experimental results. Furthermore, simulations were employed to investigate the nature of the enhancement mechanisms operative between the molecules and the semiconductor. Density functional theory (DFT) calculations suggested a charge transfer (CT) transition process between the molecules and the Cu₂O nanospheres. Three-dimensional finite-difference time domain (3D-FDTD) simulations were conducted to map out the electromagnetic field around the Cu₂O nanospheres. The experimental and simulation results have revealed the promise of the Cu₂O nanospheres as a good SERS substrate and the prospect of using the SERS substrate as a valuable tool for in situ investigation and assay of the adsorption behavior on semiconductor surfaces.

Hole transporting material (HTM) free carbon-based perovskite solar cells (C-PSCs) are one kind of promising candidates for new generation photovoltaic technology due to their superior long-term stability and low cost. However, the power conversion efficiency (PCE) of C-PSCs is significantly lower than that of HTM-based PSCs. This is mostly due to the unexpected electron recombination happening at the interface of perovskite/carbon. Moreover, the low conductivity of the carbon electrode slows down the charge collection process and results in a low fill factor and poor PCE. To address these concerns, we firstly inserted an inorganic CuSCN HTM between the perovskite and the carbon electrode to suppress the electron recombination process. Then we used a highly conductive carbon nanotube (CNT) network to form a robust interface of CuSCN/CNT and facilitate the hole collection process. As a result, the updated CuSCN and CNT incorporated C-PSCs exhibit a V_OC of 1.01 V and deliver a PCE up to 17.58% (measured in the backward scan) with pretty good reproducibility, which is the highest PCE in C-PSCs. What's more, the incorporation of CuSCN can also improve the stability of devices dramatically. The optimized device shows superior operational stability, retaining over 80% of its initial performance after 1000 h of continuous one sun illumination.

Various graphene-based Au nanocomposites have been developed as surface-enhanced Raman scattering (SERS) substrates recently. However, efficient use of SERS has been impeded by the difficulty of tuning SERS enhancement effects induced from chemical and plasmonic enhancement by different preparation methods of graphene. Herein, we developed graphene-based Au hybrids through physical sputtering gold NPs on monolayer graphene prepared by chemical vapor deposition (CVD) as a CVD-G/Au hybrid, as well as graphene oxide–gold (GO/Au) and reduced-graphene oxide (rGO/Au) hybrids prepared using the chemical in situ crystallization growth method. Plasmonic and chemical enhancements were tuned effectively by simple methods in these as-prepared graphene-based Au systems. SERS performances of CVD-G/Au, rGO/Au and GO/Au showed a gradually monotonic increasing tendency of enhancement factors (EFs) for adsorbed Rhodamine 6G (R6G) molecules, which show clear dependence on chemical bonds between graphene and Au, indicating that the chemical enhancement can be steadily controlled by chemical groups in a graphene-based Au hybrid system. Most notably, we demonstrate that the optimized GO/Au was able to detect biomolecules of adenine, which displayed high sensitivity with a detection limit of 10⁻⁷ M as well as good reproducibility and uniformity.