Environment-friendly
Tin (Sn)-based perovskite solar cells (PSCs)
have lately made significant development, showing tremendous promise
in addressing the hazardous problems associated with Pb-based PSCs.
However, even in N2 atmospheres, the thermodynamic stability
of Sn-based perovskite films and long-term stability of Sn-based PSCs
are demonstrated to be poor due to the presence of interfacial defect
trap states. Here, we demonstrate the post-treatment of Sn-based perovskite
films with ethylenediamine formate (EDAFa2) ion salt, serving
as a bi-functional interface layer to in situ passivate the interfacial
defect and improve the stability of Sn2+ by creating a
thermodynamic chemical environment pathway. Moreover, the presence
of EDAFa2 is shown to promote the interfacial energy level
alignment, which is beneficial for the charge extraction at the interface.
As a result, PSC devices with a bi-functional interface achieve a
champion power conversion efficiency (PCE) as high as 9.40% and enhanced
stability, retaining ∼95% of the original PCE stored in a N2 environment after ∼1960 h without encapsulation. This
work highlights the significant role of an interfacial design in efficient
and stable Sn-based PSCs.
Recently, low-dimensional Ruddlesden–Popper
(LDRP) perovskite-based
solar cells (PSCs) have been extensively studied because of their
robust stability. However, because of the poor conductivity of the
organic spacer, the charge transport across the spacers in the LDRP
perovskite is considerably poor, and thus regulation of the growth
orientation of LDRP cells is of primary importance. So far, the key
role of organic cations in controlling the growth orientation of LDRP
films has been widely studied, but the impact of halogens has not
been sufficiently investigated. Herein, we demonstrate the important
role of halogens in determining the characteristics of benzylamine
(BZA)-based LDRP perovskite films, where different BZAX salts (X =
Cl, Br, I) are adopted. Compared to Br and I, Cl is shown to prominently
enlarge the grain size, promote the vertical orientation, reduce the
trap state density, and prolong the carrier lifetime of LDRP film,
and all these merits effectively accelerate the carrier transport
within the film. As a result, a PSC device based on BZACl delivers
a champion PCE of 17.25% with much improved device stability. This
work unravels the vital role of Cl in regulating the crystallization
process of LDRP films, which provides a facile approach for boosting
the performance of LDRP-based PSCs.
CsPbI 3 , an all-inorganic perovskite material with suitable band gap and excellent thermal stability, has garnered significant attention for its potential in perovskite solar cells (PSCs). However, CsPbI 3 is susceptible to phase changes from photoactive to photoinactive in humid environments. Hence, it is crucial to achieve controllable growth of CsPbI 3 perovskite thin films with the desired β-crystal phase and compact morphology for efficient and stable PSCs. Herein, MAAc was used as a solvent for the CsPbI 3 precursor to fabricate β-CsPbI 3 perovskite. An intermediate compound of Cs x MA 1−x PbI x Ac 3−x was initially formed in the MAAc solution, and during annealing, the MA + and Ac − ions were replaced by Cs + and I − ions, respectively. Furthermore, the incorporation of strong C�O•••Pb coordination stabilized the black-phase β-CsPbI 3 and facilitated the growth of crystals with a narrow vertical orientation and large grain size. As a result, the PSCs with an efficiency of 18.9% and improved stability (less than 10% decay after 2000 h of storage in N 2 and less than 30% decay after 500 h of storage in humid air without any encapsulation) were achieved.
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