Passivation of organometal halide perovskites with polar molecules has been recently demonstrated to improve the photovoltaic device efficiency and stability. However, the mechanism is still elusive. Here, it is found that both polymers with large and small dipole moment of 3.7 D and 0.6 D have negligible defect passivation effect on the MAPbI 3 perovskite films as evidenced by photo thermal deflection spectroscopy. The photovoltaic devices with and without the polymer additives also have comparable power conversion efficiencies around 19%. However, devices with the additives have noticeable improvement in stability under continuous light irradiation. It is found that although the initial mobile ion concentrations are comparable in both devices with and without the additives, the additives can strongly suppress the ion migration during the device operation. This contributes to the significantly enhanced electrical-field stress tolerance of the perovskite solar cells (PVSCs). The PVSCs with polymer additives can operate up to −2 V reverse voltage bias which is much larger than the breakdown voltage of −0.5 V that has been commonly observed. This study provides insight into the role of additives in perovskites and the corresponding device degradation mechanism.

Functional additives that can interact with the perovskite precursors to form the intermediate phase have been proven essential in obtaining uniform and stable α-FAPbI 3 films. Among them, Cl-based volatile additives are the most prevalent in the literature. However, their exact role is still unclear, especially in inverted perovskite solar cells (PSCs). In this work, we have systematically studied the functions of Cl-based volatile additives and MA-based additives in formamidinium lead iodide (FAPbI 3 )based inverted PSCs. Using in situ photoluminescence, we provide clear evidence to unravel the different roles of volatile additives (NH 4 Cl, FACl, and MACl) and MA-based additives (MACl, MABr, and MAI) in the nucleation, crystallization, and phase transition of FAPbI 3 . Three different kinds of crystallization routes are proposed based on the above additives. The non-MA volatile additives (NH 4 Cl and FACl) were found to promote crystallization and lower the phase-transition temperatures. The MA-based additives could quickly induce MA-rich nuclei to form pure α-phase FAPbI 3 and dramatically reduce phase-transition temperatures. Furthermore, volatile MACl provides a unique effect on promoting the growth of secondary crystallization during annealing. The optimized solar cells with MACl can achieve an efficiency of 23.1%, which is the highest in inverted FAPbI 3 -based PSCs.

Mixed‐halide wide‐bandgap perovskites are key components for the development of high‐efficiency tandem structured devices. However, mixed‐halide perovskites usually suffer from phase‐impurity and high defect density issues, where the causes are still unclear. By using in situ photoluminescence (PL) spectroscopy, it is found that in methylammonium (MA+)‐based mixed‐halide perovskites, MAPb(I0.6Br0.4)3, the halide composition of the spin‐coated perovskite films is preferentially dominated by the bromide ions (Br−). Additional thermal energy is required to initiate the insertion of iodide ions (I−) to achieve the stoichiometric balance. Notably, by incorporating a small amount of formamidinium ions (FA+) in the precursor solution, it can effectively facilitate the I− coordination in the perovskite framework during the spin‐coating and improve the composition homogeneity of the initial small particles. The aggregation of these homogenous small particles is found to be essential to achieve uniform and high‐crystallinity perovskite film with high Br− content. As a result, high‐quality MA0.9FA0.1Pb(I0.6Br0.4)3 perovskite film with a bandgap (Eg) of 1.81 eV is achieved, along with an encouraging power‐conversion‐efficiency of 17.1% and open‐circuit voltage (Voc) of 1.21 V. This work also demonstrates the in situ PL can provide a direct observation of the dynamic of ion coordination during the perovskite crystallization.

Ion dissociation has been identified to determine the intrinsic stability of perovskite solar cells (PVSCs), but the underlying degradation mechanism is still elusive. Herein, by combining highly sensitive sub‐bandgap external quantum efficiency (s‐EQE) spectroscopy, impedance analysis, and theoretical calculations, the evolution of defect states in PVSCs during the degradation can be monitored. It is found that the degradation of PVSCs can be divided into three steps: 1) dissociation of ions from perovskite lattices, 2) migration of dissociated ions, and 3) consumption of I− by reacting with metal electrode. Importantly, step (3) is found to be crucial as it will accelerate the first two steps and lead to continuous degradation. By replacing the metal with more chemically robust indium tin oxide (ITO), it is found that the dissociated ions under light soaking will only saturate at the perovskite/ITO interface. Importantly, the dissociated ions will subsequently restore to the corresponding vacancies under dark condition to heal the perovskite and photovoltaic performance. Such shuttling of mobile ions without consumption in the ITO‐contact PVSCs results in harvesting–rest–recovery cycles in natural day/night operation. It is envisioned that the mechanism of the intrinsic perovskite material degradation reported here will lead to clearer research directions toward highly stable PVSCs.

Monolithic perovskite/organic tandem solar cells have attracted increasing attention due to their potential of being highly efficient while compatible to facile solution fabrication processes. One of the limiting factors for improving the performance of perovskite/organic tandem cells is the lack of wide‐bandgap perovskites with suitable bandgap, film quality, and optoelectronic properties for front cells. In addition, the development of low‐bandgap organic bulk‐heterojunction (BHJ) rare cells with extended absorption in the infrared range is also critical for improving tandem cells. This work has carefully optimized mixed halide wide‐bandgap perovskite (MWP) films by introducing a small amount of formamidinium (FA+) cations into the basic composition of MA1.06PbI2Br(SCN)0.12, which provides an effective means to modulate the crystallization properties and phase stability of the films. At optimized conditions, the MA0.96FA0.1PbI2Br(SCN)0.12 forms high‐quality films with grain boundaries homogeneously passivated by PbI2, leading to a reduction in defect states and an enhancement in phase stability, enabling the fabrication of perovskite solar cells with a power conversion efficiency(PCE) of 17.4%. By further integrating the MWP front cell with an organic BHJ (PM6:CH1007) rare cell composed of a nonfullerene acceptor with absorption extended to 950 nm, a tandem cell with PCE over 21% is achieved.

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Polymer hole-transport layers (HTLs) are critical components of inverted perovskite solar cells (IPVSCs). Triphenylamine derivatives PTAA (poly[bis (4-phenyl)(2,4,6-trimethylphenyl)amine]) and Poly-TPD (poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine]) have been widely adopted as hole-transport materials due to their perovskite passivation effects and suitable energy levels. However, the passivation mechanism (i.e., the functional group responsible for perovskite passivation) of triphenylamine derivative polymers remains unclear, hindering the development and application of this polymer type. Here, we develop a novel Poly-TPD derivative, S-Poly-TPD, by replacing the n-butyl functional group of Poly-TPD with an isobutyl group to explore the influence of alkyl groups on HTL performance and top-deposited perovskite properties. Compared with Poly-TPD, the increased CH 3 -terminal unit density and the decreased spatial distance between the -CH-CH 3 and -CH 2 -CH 3 units and the benzene ring in S-Poly-TPD not only enhanced the hole-transport ability but also improved the perovskite passivation effect, revealing for the first time the role of the alkyl groups in perovskite passivation. As a result, the S-Poly-TPD-based IPVSCs demonstrated high power-conversion efficiencies of 15.1% and 21.3% in

Tuberculosis (TB) is one of the major infectious diseases with the largest number of morbidity and mortality. Based on the comparison of high and low burden countries of tuberculosis in China, India and the United States, the influence of age-period-cohort on the incidence of tuberculosis in three countries from 1992 to 2017 was studied based on the Global burden of Disease Study 2017. We studied the trends using Joinpoint regression in the age-standardized incidence rate (ASIR). The regression model showed a significant decreasing behavior in China, India and the United States between 1992 and 2017. Here, we analyzed the tuberculosis incidence trends in China, India, as well as the United States and distinguished age, period and cohort effects by using age-period-cohort (APC) model. We found that the relative risks (RRs) of tuberculosis in China and India have similar trends, but the United States was found different. The period effect showed that the incidence of the three countries as a whole declines with time. The incidence of tuberculosis had increased in most age group. The older the age, the higher the risk of TB incidence. The net age effect in China and India showed a negative trend, while the cohort effect decreased from the earlier birth cohort to the recent birth cohort. Aging may lead to a continuous increase in the incidence of tuberculosis. It is related to the aging of the population and the relative decline of the immune function in the elderly. This should be timely population intervention or vaccine measures, especially for the elderly. The net cohort effect in the United States showed an unfavorable trend, mainly due to rising smoking rates and the emergence of an economic crisis. Reducing tobacco consumption can effectively reduce the incidence.