Currently, morphology optimization methods for the fused‐ring nonfullerene acceptor‐based polymer solar cells (PSCs) empirically follow the treatments originally developed in fullerene‐based systems, being unable to meet the diverse molecular structures and strong crystallinity of the nonfullerene acceptors. Herein, a new and universal morphology controlling method is developed by applying volatilizable anthracene as solid additive. The strong crystallinity of anthracene offers the possibility to restrict the over aggregation of fused‐ring nonfullerene acceptor in the process of film formation. During the kinetic process of anthracene removal in the blend under thermal annealing, donor can imbed into the remaining space of anthracene in the acceptor matrix to form well‐developed nanoscale phase separation with bi‐continuous interpenetrating networks. Consequently, the treatment of anthracene additive enables the power conversion efficiency (PCE) of PM6:Y6‐based devices to 17.02%, which is a significant improvement with regard to the PCE of 15.60% for the reference device using conventional treatments. Moreover, this morphology controlling method exhibits general application in various active layer systems to achieve better photovoltaic performance. Particularly, a remarkable PCE of 17.51% is achieved in the ternary PTQ10:Y6:PC71BM‐based PSCs processed by anthracene additive. The morphology optimization strategy established in this work can offer unprecedented opportunities to build state‐of‐the‐art PSCs.
Controlling crystal growth and reducing number of grain boundaries are crucial to maximize the charge carrier transport in organic-inorganic perovskites field-effect transistors (FETs). Herein, the crystallization and growth kinetics of...
The effects of the casting speed and solute concentration on the crystallization of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) during meniscus-guided coating (MGC) are investigated, and three morphological subregimes with increasing casting speed are identified: I) an isotropic domain-like structure; II) unidirectionally aligned crystalline bands; and III) a corrugated dendritic morphology. Interestingly, increasing the solute concentration does not affect these morphologies but merely the associated transition velocities. Numerical simulation of both the fluid dynamics in the coating bead and the crystallization itself not only explains these morphological trends but also the decrease in the width of the crystalline bands of morphology II with the casting speed. They demonstrate that the latter provides an optimal processing window for organic field-effect transistors, with minimized charge trapping, maximized on/off ratio, and reliability factor.
facile processability. [1,2] However, the application of perovskites in field-effect transistors (FETs) has received less attention and has remained challenging because of ion migration under operational conditions at room temperature due to the low formation energy of mobile ions or ionic defects in these ionic materials. [3,4] Mobile ions in perovskite FETs screen the applied gate field and reduce the gate modulation of the current yielding low fieldeffect mobility and large hysteresis. [5] In contrast, 2D Sn-based perovskites reveal favorable properties due to the insulating property of bulky organic ligands. The advantages of dielectric confinement in 2D layered structures are expected to significantly suppress ion movement in the device. [6] More importantly, the device performance can be tuned by tailoring the chemical structure of the spacer cations. [7] 2D Sn-based perovskites are promising semiconductors for high-performance FETs. [8,9] The Sn-based perovskites typically show high charge carrier mobility due to the smaller in-plane effective mass and longer carrier lifetime compared with their Pb analogs. [10] Nevertheless, there are several drawbacks to 2D Sn-based perovskite FETs. First, easy oxidation of Sn 2+ to its tetravalent state Sn 4+ , especially during solution processing, gives rise to ionic defects and leads to p-type self-doping. [11] Second, the fast Understanding and controlling the nucleation and crystallization in solutionprocessed perovskite thin films are critical to achieving high in-plane charge carrier transport in field-effect transistors (FETs). This work demonstrates a simple and effective additive engineering strategy using pentanoic acid (PA). Here, PA is introduced to both modulate the crystallization process and improve the charge carrier transport in 2D 2-thiopheneethylammonium tin iodide ((TEA) 2 SnI 4 ) perovskite FETs. It is revealed that the carboxylic group of PA is strongly coordinated to the spacer cation TEAI and [SnI 6 ] 4− framework in the perovskite precursor solution, inducing heterogeneous nucleation and lowering undesired oxidation of Sn 2+ during the film formation. These factors contribute to a reduced defect density and improved film morphology, including lower surface roughness and larger grain size, resulting in overall enhanced transistor performance. The reduced defect density and decreased ion migration lead to a higher p-channel charge carrier mobility of 0.7 cm 2 V −1 s −1 , which is more than a threefold increase compared with the control device. Temperaturedependent charge transport studies demonstrate a mobility of 2.3 cm 2 V −1 s −1 at 100 K due to the diminished ion mobility at low temperatures. This result illustrates that the additive strategy bears great potential to realize high-performance Sn-based perovskite FETs.
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