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Summary Nonfullerene acceptor (NFA) organic solar cells (OSCs) with power conversion efficiency (PCE) reaching up to 18% has shown tremendous potential toward practical applications. However, the non-radiative recombination loss in high-efficiency NFA OSCs is evidently large, and the origin remains unclear. Herein, by combining transient absorption spectroscopy, photovoltaic characterization, and detailed energy loss analysis, we unambiguously show the formation of NFA triplet exciton from free carrier recombination as a main non-radiative recombination and energy loss channel. More importantly, in contrast to the previous energetics point of view, we show side-chain fluorination in high-efficiency NFA OSCs has little effect on charge transfer energy landscapes but efficiently inhibits charge recombination to NFA triplet excitons, leading to higher V OC and PCE. Our findings provide a new view about energy loss in NFA OSCs and pave the way toward OSCs with lower V OC loss and efficiency exceeding 20%.

In cognitive radio (CR) systems, the spectrum efficiency (SE) of the secondary users (SUs) is always limited by the interference temperature constraint imposed on the primary users (PUs). Intelligent reflecting surface (IRS) has been recently proposed as a revolutionary technique which can help to enhance the SE of wireless communications. In this paper, we propose to employ an IRS to assist the SUs’ data transmission in the multiple-input multiple-output (MIMO) CR system. By jointly optimizing the transmit precoding (TPC) of the SU transmitter (ST) and the phase shifts of the IRS, we aim to maximize the achievable weighted sum rate (WSR) of SUs subject to the ST's total power, the PU's interference temperature and unit modulus constraints. To solve this complicated optimization problem in which the variables are coupled, the block coordinate descent (BCD) algorithm is introduced to alternately solve the subproblems. For each subproblem, the Lagrange dual or inner approximation method is adopted with a low complexity. Simulation results confirm the benefits of employing IRS in a MIMO CR system. The performance comparisons of the proposed algorithm with several other benchmarks are carried out by evaluating the impacts of various parameters on the WSR.

Summary Perovskite solar cells (PSCs) and organic photovoltaics (OPVs) have both undergone rapid development recently. The composition and molecular tunability of perovskite and organic semiconductors enable a large material pool with different band gaps and various physical characters, giving feasibility to construct perovskite/organic tandem solar cells (TSCs). Here, we developed a semi-empirical model, rationally selected the best available material combination, and successfully demonstrated the efficient and reproducible TSCs benefiting from their complementary band gaps and orthogonal processing solvents. Featuring with all-thermally evaporated low-loss interconnecting layers (ICLs), our 2-termimal (2T) monolithic perovskite/organic TSCs deliver high reproducibility with power conversion efficiency (PCE) narrowly distributed between 20% and 20.6% (certified as 19.54%). In addition to the promising efficiency, the UV sensitivity of OPVs is eliminated in the tandem structure, demonstrating its advantage on device stability. Those results unfold significant potentials of perovskite/organic tandem devices as reproducible and cost-effective structures to achieve high-performance TSCs.

Although the power conversion efficiencies (PCEs) of the state-of-the-art organic solar cells (OSCs) have exceeded 17%, the organic photovoltaic devices still suffer from considerable voltage losses compared with the inorganic or perovskite solar cells. Therefore, the optimization of open-circuit voltage (VOC) is of great significance for the improvement of the photovoltaic performance of OSCs. The origins of VOC have been well-established in the binary system; however, the understanding of VOC in non-fullerene acceptor (NFA)-based ternary OSCs is still lacking. Herein, we have developed a series of ternary organic photovoltaic devices, exhibiting nearly linear increased VOC as the increase of ITIC third content. We found that both the effective charge-transfer (CT) states and the nonradiative recombination losses of the bulk-heterojunction (BHJ) are altered in the ternary blends, and they collectively contribute to the tunable VOC. Our results provide a perspective for understanding the origin of VOC in NFA-based ternary OSCs.

Nonfullerene acceptors (NFAs) have attracted great attention in high-efficiency organic solar cells (OSCs). While the effect of molecular properties including structures and energetics on charge transfer has been extensively investigated, the effect of macroscopic-phase properties is yet to be revealed. Here we have performed a correlation study of the nanoscale-phase morphology on the photoexcited hole transfer (HT) process and photovoltaic performance by combining ultrafast spectroscopy with high temporal resolution and photo-induced force microscopy (PiFM) with high spatial and chemical resolution. In PM6/IT-4F, we observe biphasic HT behavior with a minor ultrafast (

Organic micropollutants have become serious threats to human health and the environment over the past years. Novel materials and technologies are urgently needed to remove environmental contaminants. Herein, spirobifluorene (SBF) and triptycene (TP) were crosslinked to produce four hierarchically porous organic polymers (NHCPs). The twisted spatial structures of the monomers endow the NHCPs with high surface areas and abundant pores, which make them suitable for removal of pollutants in aqueous solution through adsorption. According to the results from adsorption experiments, the NHCPs exhibited high removal efficiency and adsorption capacities for pollutants in solution. Particularly, NHCP-3 could remove 99.4% of bisphenol A (BPA) in a few seconds with a maximum adsorption capacity of 562 mg g−1. Furthermore, the NHCPs could be easily recovered by immersion in ethanol and recycled at least five times without a loss in efficiency.

By introducing various N‐containing compounds as efficient linkers, a series of hyper‐crosslinked porous polymers with high surface areas and gas‐uptake values were synthesized by using the Friedel–Crafts alkylation reaction. Structural characterization indicated the presence of nitrogen atoms, and gas‐sorption experiments revealed that the high gas uptake benefitted from the high surface areas and the incorporation of N‐containing linkers as Lewis basic sites. Among these porous polymers, HCP‐4 had the highest H2 uptake of 9.29 mmol g−1 at 77 K and 0.1 MPa and the highest C2H2 uptake of 6.69 mmol g−1 at 273 K and 0.1 MPa, whereas HCP‐3 showed the best CO2 uptake of 4.42 mmol g−1 at 273 K and 0.1 MPa. To understand better the important role played by nitrogen in these polymers, the isosteric heat of adsorption and adsorption selectivity of CO2 over N2 were calculated. The results showed that the triazine‐based polymer HCP‐1 had the highest CO2 over N2 selectivity of 75.4 at 295 K and 0.1 MPa, which makes it the most potential candidate for CO2 capture.

In this study, a quaternary blending strategy was applied in the fabrication of organic photovoltaic devices and large-area modules. As a result, the ultimate quaternary organic solar cells (OSCs) deliver 16.71% efficiency for small-area devices and 13.25% for large-area ( 19.34 cm 2 ) modules (certified as 12.36%), which is one of the highest efficiencies for organic solar modules to date. Our results have proved the synergistic effects of multiple components in OSCs, providing an effective strategy for achieving high-performance organic photovoltaic devices and modules.

One-dimensional (1D) small-molecule semiconducting nanostructures (NSs) have attracted more and more attention due to their unique structures and photoelectric properties. However, the preparation of real ultrafine 1D organic nanocrystals (ONCs), in which the intermolecular charge transfer (CT) is confined to a 1D direction, is still a huge challenge. Here, we report a facile way to controllably synthesize uniform 1D ONCs of μ-oxo dimeric iron(III) porphyrin [(FeTPP)2O] in a cetyltrimethyl ammonium bromide (CTAB)-assisted wet chemical reaction (WCR). In this work, the shape evolution of the (FeTPP)2O NSs was shown by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). Interestingly, the regularity and aspect ratio of the (FeTPP)2O 1D NCs increased with time, while their diameters decreased. Further experiments proved that this was closely associated to the reconstruction of the CTAB micelles. After optimizing the experimental conditions, we not only synthesized uniform 1D ONCs with a width of ∼28 nm and/or an aspect ratio of ∼37, but also obtained 2D ONCs with a thickness of about 10 nm. Here, the finest 1D ONCs that we have seen to date have been prepared. The corresponding UV-vis absorption and photoluminescence (PL) spectra are enhanced with a decrease in the diameter and an increase in the aspect ratio of (FeTPP)2O 1D ONCs with high crystallinity, which clearly shows the first report of the confinement effect of the intermolecular CT state in 1D ONCs. This work paves a new route to prepare 1D ONCs and provides us with a chance to further understand and apply the intermolecular CT in 1D organic photoelectrical devices.

This paper proposed a robust spatial spectrum sensing algorithm to apply to a communication scenario which exist the estimated error of noise power and the jamming. A modified approximate model is proposed to include the estimated error of noise power and the jamming. The corresponding performance indicators are proposed. The proposed robust algorithm estimates the estimated error vector of noise power and the jamming vector, independently. The estimated error vector of noise power and the jamming vector are separated from model coefficient vector, and the influence of estimated error and jamming is mitigated. The robustness of proposed algorithm is achieved. Simulation results show that the proposed robust algorithm has best sensing performances, and best accuracy of PU estimation, comparing with other sparsity algorithms. The sensing performances of proposed robust algorithm are not easy to be affected by the sampling rate of secondary users. When the sampling rate of secondary users or SNR is increasing, these sensing performances of proposed robust algorithm are also increasing.

In this paper, a positioning system is designed based on the visible light communication (VLC) technology for the tracking of mobile target in the indoor environment. The practical received signal strength (RSS) can be measured for subsequent positioning algorithm by using the designed system. Based on the practical measurements, an empirical equation is proposed to estimate the target's distances relative to the referenced LEDs. Then, taking advantage of the relative distances, the location estimation can be obtained by the trilateration method. Furthermore, Kalman Filter is used for improving the positioning result computed by trilateration method. Finally, experimental results show that the average location errors by adopting the derived empirical formula and trilateration can reach to 3.4cm, and the accuracy of positioning can be promoted to 2.6cm by using Kalman Filter in a real wireless environment.

In this paper, a three-dimensional (3-D) positioning system using fingerprinting and K-Nearest neighbor is proposed. The implementation of the proposed positioning system based on visible light communication (VLC) is discussed. On-off keying (OOK) modulation, Manchester coding and time division multiplexing (TDM) are utilized to obtain both lossless data and accurate received signal strength indications (RSSIs) without sacrificing the comfort of indoor illumination. The proposed 3-D positioning algorithm is conducted in three processes. Firstly, we quickly traverse all sampling points in the fingerprint database to find the nearest neighbor and choose candidate sampling points around the nearest neighbor. Secondly, we conduct an iterative search among candidate sampling points to find K-Nearest neighbors. Finally, we obtain estimated coordinates using weighted average method. Experimental result shows that, the proposed system possesses fast location and high accuracy.