Semiconducting molecules have been employed to passivate traps extant in the perovskite film for enhancement of perovskite solar cells (PSCs) efficiency and stability. A molecular design strategy to passivate the defects both on the surface and interior of the CH3NH3PbI3 perovskite layer, using two phthalocyanine (Pc) molecules (NP‐SC6‐ZnPc and NP‐SC6‐TiOPc) is demonstrated. The presence of lone electron pairs on S, N, and O atoms of the Pc molecular structures provides the opportunity for Lewis acid–base interactions with under‐coordinated Pb2+ sites, leading to efficient defect passivation of the perovskite layer. The tendency of both NP‐SC6‐ZnPc and NP‐SC6‐TiOPc to relax on the PbI2 terminated surface of the perovskite layer is also studied using density functional theory (DFT) calculations. The morphology of the perovskite layer is improved due to employing the Pc passivation strategy, resulting in high‐quality thin films with a dense and compact structure and lower surface roughness. Using NP‐SC6‐ZnPc and NP‐SC6‐TiOPc as passivating agents, it is observed considerably enhanced power conversion efficiencies (PCEs), from 17.67% for the PSCs based on the pristine perovskite film to 19.39% for NP‐SC6‐TiOPc passivated devices. Moreover, PSCs fabricated based on the Pc passivation method present a remarkable stability under conditions of high moisture and temperature levels.
The search for new classes of organic and metal-organic compounds for organic thin-film transistors (OTFTs) is of immense current interest due to the relatively low cost and potential applications of OTFTs in flexible large-area electronic devices such as displays [1,2] and sensors.[3±5] Indeed,OTFTs have been recently reported in the fabrication of active-matrix displays [6] and integrated circuits (ICs) for logic and memory chips. [7] Unlike their silicon-based TFTs counterparts which require expensive and complicated fabricating systems at a high temperature, [8] the deposition of organic materials on large-area substrates, including flexible polymer substrates, is much less complicated.[1]Over the last decade, much attention has been focused on the study of pentacene and its derivatives as organic semiconductors for OTFTs. This class of materials has been shown to exhibit excellent field-effect mobilities [9] and environmental stabilities.[1] Similarly, oligothiophenes, [10] poly(3-alkyl-thiophene) (P3HT), [11] and fused heterocyclic compounds [12] have been shown to possess comparable properties that are highly desirable for OTFT applications. Despite these advances, difficulties in structural modification of these literature-reported organic semiconductors remain. Current methods used to modify charge-carrier properties of the materials rely on changing the type of substitution on the materials. By introducing electron-donating (D) or electron-accepting (A) functional groups, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) levels of the materials can be fine-tuned to give either p-type or n-type organic semiconductors. In this context, it would be desirable to develop new classes of organic materials which possess extended p-conjugated electronic systems that can be easily prepared and modified and exhibit effective intermolecular interactions for charge transportation. Work in our laboratory and by others has demonstrated the potential applications of conjugated ethynylated arylacetylene materials such as arylacetylenes, [13] poly(arylene ethylene)s, [14] and metal-containing acetylide complexes. [15] These materials have received considerable attention in organic light-emitting diodes, [16] optoelectronics, [17] molecular electronics, [18] and sensors. [19] Through incorporation of different electron-donating or electron-withdrawing functional groups, the physical and electronic behavior of oligomeric arylacetylenes such as thermal stabilities, carrier transport, and structural packing properties could be readily and systematically modified for OTFT applications. Also, the p-conjugation length of the linear molecules can easily be extended by synthetically controlling the number of repeating arylacetylene moieties incorporated into the structures. For example, Wong et al. recently reported the synthesis of crystalline pyrimidine-containing arylethynyl molecules with dipole±dipole and face-to-face p±p interactions. [20] Indeed, the relative pl...
We demonstrate a molecular design strategy to enhance the efficiency of phthalocyanine (Pc)-based holetransporting materials (HTMs) in perovskite solar cells (PSCs). Herein, two titanyl phthalocyanine (TiOPc) derivatives are designed and applied as dopant-free HTMs in planar n-i-p-structured PSCs. The newly developed TiOPc compounds possess eight n-hexylthio groups attached to either peripheral (P-SC 6 -TiOPc) or nonperipheral (NP-SC 6 -TiOPc) positions of the Pc ring. Utilizing these dopant-free HTMs in PSCs with a mixed cation perovskite as the lightabsorbing material and tin oxide (SnO 2 ) as the electrontransporting material (ETM) results in a considerably enhanced efficiency for NP-SC 6 -TiOPc-based devices compared to PSCs using P-SC 6 -TiOPc. Hence, all of the photovoltaic parameters, including power conversion efficiency (PCE), fill factor, open-circuit voltage, and short-circuit current density, are remarkably improved from 5.33 ± 1.01%, 33.34 ± 3.45%, 0.92 ± 0.18 V, and 17.33 ± 2.08 mA cm −2 to 15.83 ± 0.44%, 69.03 ± 1.59%, 1.05 ± 0.01 V, and 21.80 ± 0.36 mA cm −2 , respectively, when using the nonperipheral-substituted TiOPc derivative as the HTM in a PSC. Experimental and computational analysis suggests more compact molecular packing for NP-SC 6 -TiOPc than P-SC 6 -TiOPc in the solid state due to stronger π−π interactions, leading to thin films with better quality and higher performance in hole extraction and transportation. PSCs with NP-SC 6 -TiOPc also offer much higher long-term stability than P-SC 6 -TiOPc-based devices under ambient conditions with a relative humidity of 75%.
Importance of alkyl chain-length on the self-assembly of new Ni(qdt) 2 complexes and charge transport properties3
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