developed silicon solar cells. It shows the great potential of PSCs as the dominator of next-generation photovoltaics. Whereas, during the evolution of PSC development, the metal oxide electron transporting layer (ETL), as well as the ETL/perovskite interface, [11][12][13][14] has always been an issue in regard to photovoltaic efficiency and device stability. [8] Derived from dye-sensitized solar cells (DSSCs), the combination of compact and mesoporous TiO 2 has been commonly utilized as ETLs during the early studies of PSCs. [15] But a high sintering temperature of ≈500 °C is normally required for the fabrication process, which is high energy consumption and incompatible with scalable depositions on flexible substrates. Worse still, TiO 2 is highly photocatalytic active under ultraviolet (UV) irradiation that severely hampers the long-term stability of PSCs under illumination. [16][17][18][19][20][21][22] Later on, a new ETL, SnO 2 , has been developed as a better candidate, due to its low-temperature processability [23] and high sustainability under UV illumination. [24][25][26][27] More importantly, SnO 2 film has superior crystallinity and carrier mobility in comparison to TiO 2 . [28,29] Thus, a single layer of compact SnO 2 could enable an efficient charge transport and suppressed recombination losses at the ETL/perovskite interface. Benefiting from these advantages, PSCs based on SnO 2 as ETL have reached PCE of 25.2% to date. [30] Whereas, considerable amount of oxygen vacancies on the SnO 2 surface would act as deep traps to capture the photogenerated carriers, which causes hysteresis and instability of the device. [31][32][33][34] And this intrinsic defect of SnO 2 needs to be resolved for a further PCE breakthrough of PSCs.In recent years, significant attempts of defect-passivation have been made to decrease the oxygen vacancies and trap states on SnO 2 surface. [35][36][37][38] Among them, n-type fullerene derivatives represent one of the most studied and efficacious passivator, [39][40][41][42] due to the ease of forming coordinate bonds between carboxylate group and SnO 2 surface. In addition, fullerene derivative is a common electron acceptor in organic solar cells (OSCs), [43] which grants an effective electron extraction from the perovskite active layer to ETL, thus contributing to higher PSC performances. Nevertheless, it should be noticed that π-cage structures of fullerene derivatives are prone to self-aggregate, [44] which strongly affects the validity and SnO 2 has been universally applied as electron transporting layer (ETL) towards the fabrication of highly efficient perovskite solar cells (PSCs), owing to its unique advantages including low-temperature solution-processability, high optical, transmittance and good electrical conductivity. Uncoordinated Sn-dangling bonds on SnO 2 surface exist as deep traps to capture the photogenerated carriers, causing hysteresis and device instability. Fullerene derivatives, though being widely utilized as the passivator for SnO 2 , are highly prone to...

As a single-element nanomaterial, sulfur nanodots are emerging as a kind of heavy-metal-free nanomaterials which are believed to excel over traditional undesirable compound semiconductor nanocrystals in practical applications. Attaining their potential shall rest on the facile fabrication of high quality samples. Yet, so far the reported fabrication techniques for fluorescent sulfur nanodots have been time-consuming and cost-ineffective. Instead, we employed a strategy of hydrothermal reaction to synthesize sulfur nanodots, which reduces the synthesis time remarkably from generally required 125 h to 4 h. As-synthesized sulfur nanodots (without any post-treatment) manifest good monodispersity and a reasonable photoluminescence quantum yield up to 4.02%. The fission-aggregation mechanism has been proposed to account for the reaction dynamics in the formation of sulfur nanodots. Optical spectroscopic analysis indicates the existence of tail states in the electronic structures of sulfur nanodots, and the photoluminescence properties are governed by both the core and surface states of the sulfur nanodots, which may provide usable hints for manipulating and harnessing the luminescence properties. Besides the insight into both the synthesis and emission mechanism of luminescent sulfur nanodots, our findings pave the way to the bio-related expedite exploitation of these materials.

Dimers made of noble metal particles possess extraordinary field enhancements but suffer from large dissipation, whereas low-loss dielectric dimers are limited by relatively weak optical confinement. Hybrid systems could take advantages from both worlds. In this contribution, we study the mode coupling in a hybrid dimer with rigorous dipole−dipole interaction theory and explore its potential in fluorescence enhancement. We first discovered that the direct coupling between metal surface−plasmon resonance and dielectric electric−dipole mode creates a hybridized mode due to the strong electric−electric dipole−dipole interaction between the constituent nanoparticles, whereas the dielectric magnetic−dipole mode can only indirectly couple to the plasmons on the basis of the induced electric−magnetic dipole−dipole interaction. When an electric/magnetic quantum emitter couples to the hybrid dimer, the emitter selectively excites the electric/magnetic (magnetic/electric) resonant modes of the dimer for emitter orientation parallel (perpendicular) to the dimer axis. Our study shows that the hybrid dimer simultaneously possesses high field enhancement and low-loss features, which demonstrates a fluorescence excitation rate 40% higher than that of the pure dielectric dimer and an average quantum yield 30% higher than that of the pure metallic dimer. On top of that, the unique asymmetrical structure of the hybrid dimer directs 20% more radiation toward the dielectric side, hence improving the directivity of the dimer as an antenna.

In this Letter, the optical properties of randomly positioned silicon nanowire arrays are studied. The result shows that position randomization with a filling ratio larger than 36% renders better absorptance over a broadband ranging from 300 to 1130 nm compared to regular structures. The ultimate efficiency of a 48% filling ratio position randomized nanowire structure is 13.4% higher compared to the optimized regularly arranged nanowire structure with the same thickness. The absorptance enhancement of random structures is attributed to lowered reflectance, more supported resonant modes, and broadening of existing resonance.

In this paper, the optical properties of the silicon nano-cone-hole (NCH) structure array are studied. The ultimate efficiency of the optimized NCH array is enhanced by 23.11% compared to an optimized nanohole array of the same thickness. The absorptance enhancement of the NCH arrays is attributed to its lowered reflectance, more supported resonant modes, and enhanced mode interaction. The angular dependence of ultimate efficiency is also investigated.