NDI‐Based Small Molecule as Promising Nonfullerene Acceptor for Solution‐Processed Organic Photovoltaics

Abstract

nonfullerene electron-accepting and electron-transporting materials is desirable to enhance the performance of OPVs. [35][36][37] Recently, several groups have reported novel nonfullerene small molecules as electron acceptors in solution-processed OPVs. [38][39][40][41][42][43][44][45][46][47][48][49] Among these materials, perylene diimide derivatives (PDIs) have widely been investigated [50][51][52][53][54][55] and have achieved power conversion effi ciencies (PCEs) as high as 6%. [52][53][54][55] However, since the high planarity and strong intermolecular interactions of PDIs lead to large-scale phase separation, one has to suppress the crystallinity of PDIs at the expense of electron mobility. [ 35,51 ] The greatest challenge in developing more effi cient nonfullerene acceptors in OPVs is the lack of good electron-transporting semiconductors that integrate solution processability with suitable energy levels and transport properties of the acceptors, and with molecular characteristics that can optimize the morphology. Naphthalene diimides (NDIs), similar to PDIs, are extensively utilized as dye materials, providing a unique variability in structure modifi cation and a widely tunable absorption. [56][57][58][59][60] However, compared with PDI-based small molecules, NDI-based small molecules have not been extensively studied as acceptors in OPVs, with the exception of the NDI-thiophene oligomers reported by Sauvé and co-workers [ 61,62 ] and Jenekhe and co-workers, [ 63,64 ] which showed highest PCEs of 1.5%. NDI is a versatile electron-defi cient building block that has been employed as a high electron mobility semiconductor. [ 65 ] Here, we designed and synthesized a novel dimer of NDI (BiNDI) using a vinyl linker ( Figure 1 A), which can extend the conjugation length, planarize the molecular backbone, and enhance the intermolecular π-π stacking. BiNDI exhibited an excellent electron transport property with a highest electron mobility of 0.365 cm 2 V −1 s −1 . OPVs by using BiNDI as the acceptor showed a highest PCE of 2.41%, which is the best result for NDI-based small molecular acceptors. Results and Discussion Material Synthesis and CharacterizationAs shown in Figure 1 A, BiNDI was synthesized by Stille coupling of monobromo-NDI and trans-1,2-bis(tributylstannyl) ethane in the presence of Pd(PPh 3 ) 4 . The reaction product is A novel naphthalene diimide (NDI)-based small molecule (BiNDI) is designed and synthesized by linking two NDI monomers via a vinyl donor moiety. The electronic structure of BiNDI is carefully investigated by ultraviolet photoelectron spectroscopy (UPS). Density functional theory (DFT) sheds further light on the molecular confi guration and energy level distribution. Thin fi lm transistors (TFT) based on BiNDI show a highest electron mobility of 0.365 cm 2 V −1 s −1 in ambient atmosphere. Organic photovoltaics (OPVs) by using BiNDI as the acceptor show a highest power conversion effi cency (PCE) of 2.41%, which is the best result for NDI-based small molecular acceptors. Transmission el...

Naphtho[2,3-b]thiophene diimide (NTI): a mono-functionalisable core-extended naphthalene diimide for electron-deficient architectures

“…S7 and Table S2, S3, ESI †, PCE for PTB7-Th/4b: 1.9%, PTB7-Th/5b: 2.5%). Note that these performances are similar to those of the NDI-based small molecule recently developed, 14 which implies that NTI is a promising building block for non-fullerene acceptors. In summary, we have successfully synthesized naphtho[2, 3-b]thiophene diimide (NTI).…”

Recent Advances in Nonfullerene Acceptors for Organic Solar Cells

“…The PCE performance about 1.24% of PBDTTT‐C‐T was the highest among all the devices. In 2015, Russell group developed a novel nonfullerene small molecule acceptor T52 that the linker between the two NDI molecules was replaced by the vinyl group . This T52 molecule possessed an extended absorption region from 350 to 500 nm and the HOMO and LUMO energy levels were −6.74 and −4.35 eV, respectively.…”

A Triphenylamine–Naphthalenediimide–Fullerene Triad: Synthesis, Photoinduced Charge Separation and Solution‐Processable Bulk Heterojunction Solar Cells

“…[15,16] NDI derivativesh ave attracted considerable interest as electron acceptors in photoinduced chargeseparation [17][18][19][20][21] and in the fabrication of organic electronic devices. [22,23] Incorporation of electron-withdrawing subunits at the core of NDIs has been shown to significantly improve the efficiency of BHJ devicesi f blendedw ith the conventional donorp olymer P3HT. [24][25][26][27][28] The enhanced efficiency of the new targetsc ontaining an NDI core is mainly due to extended conjugation,anincreaseinlight-harvesting, and intermolecular p-p stacking.…”