Photovoltaics based on metal halide perovskites have recently achieved a certificated efficiency of 25.2%. One of the factors that limit further development of these devices comes from the defective boundaries between crystalline domains in perovskite solar cells (PSCs). Such boundaries represent a significant loss channel causing nonradiative recombination, but systematic optimization procedures have not been developed yet to control their properties. Herein, we propose a facile but effective defect healing method to passivate the defects along the grain boundaries in PSCs by post-treatment of formamidinium iodide (FAI) solution in isopropyl alcohol (IPA). We use a combination of methods including space-charge-limited current, steady-state and time-resolved photoluminescence, confocal laser scanning microscopy, and transient absorption spectroscopy to show the reduction of density of defect states in perovskite films processed with 1 mg/mL FAI solution. The resultant FAI healed PSCs achieve an average power conversion efficiency of 19.26% (with a champion efficiency of 20.62%), higher than that of 16.45% in the control cell. FAI healed devices without encapsulation maintain nearly 95% of the initial efficiency after 60-day storage under N 2 environment and nearly 78% of the initial efficiency after 30-day storage under the ambient condition with varied humidity. Our results demonstrate that FAI healing is an effective way to passivate the defect states along grain boundaries for high-efficiency and stable PSCs.

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The controlled crystallization process is of significance to the morphological quality of wide-band-gap perovskite absorbers, especially with excessive bromide ions. Moreover, the non-radiative recombination assisted by surface defects is one of the major unfavorable factors that confines the development of highly efficient wide-band-gap perovskite solar cells (PSCs). Here, 1.65 eV wide-band-gap PSCs are constructed by a sequential deposition method with tailored morphology of highly reproducible perovskite absorbers. The controlled crystallization with the help of NH 4 Cl enables the perovskite films with larger and more uniform grains, which result in less bulk defects. At the same time, (NH 4 ) 2 SO 4 as a passivation layer reduces the uncoordinated Pb 2+ and Pb 0 defects on the surface of the perovskite film and improves the hydrophobicity due to newly formed insoluble PbSO 4 . Eventually, the synergistic effect of ammonium salts results in a high V OC of 1.18 V and an optimal efficiency of 20.43%, which is one of the highest power conversion efficiencies for 1.65 eV wide-band-gap-based PSCs constructed by a two-step deposition process. This work confirms that the sequential deposition method and addition of proper ammonium salts are effective strategies toward highly efficient and stable wide-band-gap PSCs.

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In this work, we have studied the optimal spectrum sensing interval, which is the time between two consecutive spectrum sensing activities, such that the delay of the cognitive transmission is minimized. The throughput maximization of the cognitive radio is always a common goal of the researchers, which is keenly related to the delay of the cognitive transmission. Whereas the delay is mostly decided by the spectrum sensing interval for a given primary user (PU) channel. Therefore, we have studied the setting of the spectrum sensing interval to minimize the transmission delay of the secondary user (SU). Especially, the retransmission is considered, which deteriorates the delay of the cognitive transmission; however, neglected by the most studies. Finally, we provide both the optimal setting of the spectrum sensing interval and the numerical values.