The high polarity of water molecules inevitably causes the decomposition of perovskites. We retard the degradation by introducing an ultrathin ALD–Al2O3layer, which has almost no negative effect on performance.
Organic-inorganic halide perovskites have emerged as attractive materials for use in photovoltaic cells. Owing to the existence of dangling bonds at the grain boundaries between perovskite crystals, minimizing the charge recombination at the surface or grain boundaries by passivating these trap states has been identified to be one of the most important strategies for further optimization of device performance. Previous reports have mainly focused on surface passivation by inserting special materials such as graphene or fullerene between the electron transfer layer and the perovskite film. Here, we report an enhanced efficiency of mesoscopic perovskite solar cells by using graphene quantum dots (GQDs) to passivate the grain boundaries of CHNHPbI. The highest efficiency (17.62%) is achieved via decoration with 7% GQDs, which is an 8.2% enhancement with respect to a pure perovskite based device. Various analyses including electrochemical impedance spectroscopy, time-resolved photoluminescence decay and open-circuit voltage decay measurements are employed in investigating the mechanism behind the improvement in device performance. The findings reveal two important roles played by GQDs in promoting the performance of perovskite solar cells - that GQDs are conducive to facilitating electron extraction and can effectively passivate the electron traps at the perovskite grain boundaries.
The DMAC-based deposition–crystallization method allows control over the dynamics of CH3NH3PbI3 grain growth for the realization of high efficiency devices.
We report here the tentative discovery of a Jovian planet in orbit around the rapidly pulsating subdwarf B-type (sdB-type) eclipsing binary NY Vir. By using new determined eclipse times together with those collected from the literature, we detect that the observed-calculated (O-C) curve of NY Vir shows a smallamplitude cyclic variation with a period of 7.9 years and a semiamplitude of 6.1 s, while it undergoes a downward parabolic change (revealing a period decrease at a rate ofṖ = −9.2 × 10 −12 ). The periodic variation was analyzed for the lighttravel time effect via the presence of a third body. The mass of the tertiary companion was determined to be M 3 sin i ′ = 2.3(±0.3) M Jupiter when a total mass of 0.60 M ⊙ for NY Vir is adopted. This suggests that it is most probably a giant circumbinary planet orbiting NY Vir at a distance of about 3.3 astronomical units (AU). Since the rate of period decrease can not be explained by true angular momentum loss caused by gravitational radiation or/and magnetic braking, the observed downward parabolic change in the O-C diagram may be only a part of a long-period (longer than 15 years) cyclic variation, which may reveal the presence of another Jovian planet (∼ 2.5M Jupiter ) in the system.
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