Two-step-fabricated FAPbI 3 -based perovskites have attracted increasing attention because of their excellent film quality and reproducibility. However, the underlying film formation mechanism remains mysterious. Here, the crystallization kinetics of a benchmark FAPbI 3 -based perovskite film with sequential A-site doping of Cs + and GA + is revealed by in situ X-ray scattering and first-principles calculations. Incorporating Cs + in the first step induces an alternative pathway from δ-CsPbI 3 to perovskite α-phase, which is energetically more favorable than the conventional pathways from PbI 2 . However, pinholes are formed due to the nonuniform nucleation with sparse δ-CsPbI 3 crystals. Fortunately, incorporating GA + in the second step can not only promote the phase transition from δ-CsPbI 3 to the perovskite α-phase, but also eliminate pinholes via Ostwald ripening and enhanced grain boundary migration, thus boosting efficiencies of perovskite solar cells over 23%. This work demonstrates the unprecedented advantage of the two-step process over the one-step process, allowing a precise control of the perovskite crystallization kinetics by decoupling the crystal nucleation and growth process.
Linjiang Yu,Jia Dong,Mingyang Tang,Yi Liu,Fei Wu,Yan Yan,Gang Liu,Chunlin Song
A conventional preparation method of electroceramics was used to synthesise Pb-free 0.85Na 0.5 Bi 0.5 TiO 3 -0.15CaTiO 3 - x La (NBT-CT- x La) ceramics. La 3+ doping effectively refined the grains and enhanced the dielectric breakdown strength (BDS) of the ceramics; this result was confirmed by numerical simulations, which revealed that grain refinement significantly contributed to the enhancement of the BDS. The energy storage density consequently improved when an appropriate amount of La 3+ was added to the NBT-CT ceramics. In particular, the NBT-CT-0.75La ceramic displayed a maximum energy storage density of 2.15 J/cm 3 and a high BDS of 210 kV/cm. This ceramic also possessed relatively excellent temperature and frequency stabilities (30–150 °C, 0.2–200 Hz). Moreover, the ceramics exhibited exceptional charge–discharge performances, with an outstanding power density of 43.87 MW/cm 3 , which is nearly twice of that of other NBT-based ceramics. On the basis of the findings, the NBT-CT-0.75La ceramic can be considered to be a promising candidate material for the pulsed power application.
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