Passivation of electronic defects
on the surface and at grain boundaries
(GBs) of perovskite films has become one of the most effective tactics
to suppress charge recombination in perovskite solar cells. It is
demonstrated that trap states can be effectively passivated by Lewis
acid or base functional groups. In this work, nicotinamide (NTM, commonly
known as vitamin B3 or vitamin PP) serving as a Lewis base additive
is introduced into the PbI2 and/or FAI: MABr: MACl precursor
solution to obtain NTM modified perovskite films. It has been found
that the NTM in the perovskite film can well passivate surface and
GBs defects, control the film morphology and enhance the crystallinity
via its interaction with a lone pair of electrons in nitrogen. In
the presence of the NTM additive, we obtained enlarged perovskite
crystal grain about 3.6 μm and a champion planar perovskite
solar cell with efficiency of 21.72% and negligible hysteresis. Our
findings provide an effective route for crystal growth and defect
passivation to bring further increases on both efficiency and stability
of perovskite solar cells.
Cesium (Cs) contained triple-cation and mixed halide perovskite (CsFAMA) is broadly employed as light absorption layers for efficient and stable perovskite solar cells (PSCs) fabrication with high reproducibility. On the other hand, thermal annealing is a universal posttreatment method for perovskite films preparation. Moreover, thermal management highly depends on perovskite materials. However, no specialized study has been reported on CsFAMA perovskite to date. Herein, we have systematically investigated the influence of thermal annealing and annealing time on CsFAMA films and their solar cells. We demonstrated that heating time of 45 or 60 min at 100 °C is desirable. More interestingly, we found that the unannealed CsFAMA films exhibit ultrahigh photoluminescence (PL) intensities, much stronger than that of annealed films. Note that PL intensities gradually weaken as a function of annealing time. In particular, the PL intensities of fresh films (after antisolvent dripping) are at least 200 times higher than that of 60 min annealed films. To our knowledge, it is the first time to report this PL behavior. We speculate that it is due to quantum confinement effect of perovskite crystal nuclei and "cage effect" of DMSO intermediates in the fresh films. To this point, the unannealed CsFAMA films may have great potential in PL emission applications.
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