Hole transporting materials (HTMs) play a crucial role in achieving highly efficient and stable perovskite solar cells (PSCs). Spirotyped materials being the most widely used HTMs are commonly utilized with dopants, such as Li-TFSI, to improve their carrier mobility significantly. However, dopants could affect the morphology of hole transporting layer negatively by forming defects and pinholes which restrict the performance of devices. Here, we adopt the extended πconjugated structures N-ethylcarbazole and dibenzothiophene to substitute the donor group 4-methoxyphenyl of spiro-OMeTAD, devising two novel HTMs, SC and ST, respectively. Notably, SC possesses low crystallinity and good solubility due to the existence of ethyl in side groups, leading to decent miscibility with Li-TFSI to prevent unfavorable phase-separation. The SC-based device delivers the best power conversion efficiency (PCE) of 21.76% which is higher than that of spiro-OMeTAD (20.73%), attributed to the formation of smooth and pinhole-free morphology. Moreover, it exhibits long-term stability and retains over 90% of initial PCE value for more than 30 days without encapsulation in ambient air. In contrast, the STbased device suffers from dense pinholes induced by its relatively high crystallinity and poor solubility, resulting in a low PCE of 18.18% and inferior stability. Thus, it is effective to modify the side groups in spiro-typed HTMs with specific structures to obtain predictable properties, fabricating PSCs with high efficiency and stability facilely.
The two-dimensional
(2D)/three-dimensional
(3D) heterojunction perovskite solar cell (PSC) has recently been
recognized as a promising photovoltaic structure for achieving high
efficiency and long-term stability. Rational design of the 2D spacer
cation is important to achieve a win–win situation for defects’
passivation and photogenerated carrier extraction. Herein, we carry
out first-principles calculation to analyze the dipole moment of phenethylamine-type
molecules and their resulting 2D/3D perovskites. Based on the results
of theoretical calculation, the dipole moment of 2D cations can be
well tuned by varying the number of fluorine atoms on the para-position
of the benzene ring, which further determines the interfacial dipole
across the 2D/3D heterojunction interface. A high dipole 2D perovskite
layer at the interface between the 3D perovskite and hole-transporting
material is found to promote charge transport and suppress charge
trapping efficiently. As a result, our 2D/3D PSCs exhibit a champion
power conversion efficiency over 22% and a fill factor over 83%. Moreover,
our solar cells also show a remarkable stability, maintaining 80%
of its initial efficiency for more than 1400 h without encapsulation
under a 30 ± 5% relative humidity.
The stacking of 2D perovskites on the top of 3D perovskites has been recognized as a promising interfacial treatment approach to improve the stability and efficiency of planar perovskite solar...
Although incorporating multiple halogen (bromine) anions and alkali (rubidium) cations can improve the open‐circuit voltage (Voc) of perovskite solar cells (PSCs), severe voltage loss and poor stability have remained pivotal limitations to their further commercialization. In this study, acetylcholine (ACh+) is anchored to the surface of a quadruple‐cation perovskite to provide additional electron states near the valence band maximum of the perovskite surface, thereby enhancing the band alignment and minimizing the Voc loss significantly. Moreover, the quaternary ammonium and carbonyl units of ACh+ passivate the antisite and vacancy defects of the organic/inorganic hybrid perovskite. Because of strong interactions between ACh+ and the perovskite, the formation of lead clusters and the migration of halogen anions in the perovskite film are suppressed. As a result, the device prepared with ACh+ post‐treatment delivers a power conversion efficiency (PCE) (21.56%) and a value of Voc (1.21 V) that are much higher than those of the pristine device, along with a twofold decrease in the hysteresis index. After storage for 720 h in humid air, the device subjected to ACh+ treatment maintained 70% of its initial PCE. Thus, post‐treatment with ACh+ appears to be a useful strategy for preparing efficient and stable PSCs.
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