Linna Zhu

Aggregation-Induced Emission and Aggregation-Promoted Photo-oxidation in Thiophene-Substituted Tetraphenylethylene Derivative.

Aggregation-induced emission combined with aggregation-promoted photo-oxidation has been reported only in two works quite recently. In fact, this phenomenon is not commonly observed for AIE-active molecules. In this work, a new tetraphenylethylene derivative (TPE-4T) with aggregation-induced emission (AIE) and aggregation-promoted photo-oxidation was synthesized and investigated. The pristine TPE-4T film exhibits strong bluish-green emission, which turns to quite weak yellow emission after UV irradiation. Interestingly, after solvent treatment, the weakly fluorescent intermediate will become bright-yellow emitting. Moreover, the morphology of the TPE-4T film could be regulated by UV irradiation. The wettability of the TPE-4T microcrystalline surface is drastically changed from hydrophobic to hydrophilic. This work contributes a new member to the aggregation induced photo-oxidation family and enriches the photo-oxidation study of tetraphenylethylene derivatives.

Efficient small-molecule non-fullerene electron transporting materials for high-performance inverted perovskite solar cells

Two π-conjugated small molecules based on the multifused rigid ladder-type backbone of ITCPTC are employed as the electron transporting materials in inverted perovskite solar cells. The two compounds are distinguished by the side chain thiophene and selenophene groups. Their energy levels match well with perovskite materials. Results demonstrate that the thiophene side chain endows ITCPTC-Th with smoother morphology, higher electron mobility, and more efficient electron extraction and electron transporting properties. Inverted PSCs with the ITCPTC-Th electron transporting material (ETL) show a high efficiency of 17.11%, which is higher than the efficiency of 16.12% obtained from the ITCPTC-Se-based PSCs. Notably, the performances of the ITCPTC-based ETLs are slightly higher than those of PCBM (with the highest PCE of 15.97%) under identical conditions. In addition, the two compounds also show excellent performance when applied as the interlayer between perovskite and the C60 electron transporting layer. High efficiencies approaching 19% are obtained in devices containing the ITCPTC interlayers, further confirming their decent electron transporting properties. The ITCPTC compounds thus have great potential as efficient alternatives for the expensive PCBM ETL in inverted perovskite solar cells.

Fluorescent nanofiber film based on a simple organogelator for highly efficient detection of TFA vapour

A new organogelator SYW without common auxiliary groups was synthesized and characterized, and its gelation properties were systematically studied. SYW preferably gelatinized from aromatic solvents, and in these cases formed stable organogels. The emission of light from SYW was very weak in solution but significantly stronger in the gel state, i.e., showing typical gelation-induced emission enhancement (GIEE). In particular, the xerogel film showed bright yellow emission and could be used for detecting trifluoroacetic acid (TFA) vapor. The fibrous film exhibited high sensitivity to this vapor, and the detection limit was estimated to be quite low, at 3.2 ppb. Reports of organogeltors lacking normal auxiliary groups yet still able to form gels and detect certain species have been rare, so the current work on SYW enriches the study of organogels.

A pseudo-two-dimensional conjugated polysquaraine: an efficient p-type polymer semiconductor for organic photovoltaics and perovskite solar cells

In this paper, an efficient p-type polymer semiconductor (PASQ-IDT) is first developed by integrating a two-dimensional (2D) structure concept into the design of squaraine-based π-conjugated polymers, and it shows multiple applications in both bulk-heterojunction polymer solar cells (BHJ-PSCs) and perovskite solar cells (PVSCs) with high performance. As the polymer-donor blended with a fullerene acceptor, PASQ-IDT can endow the derived additive-free single-junction PSCs and semi-transparent PSCs with impressive efficiencies of 6.35% and 4.03%, respectively, both of which are the highest values reported for polysquaraines. More encouragingly, PASQ-IDT not only exhibits good hole extraction/transport ability, but also shows very good surface wettability to the perovskite precursor solution to enable the growth of perovskites with high film quality, making it suitable as an efficient hole transporting material (HTM) for inverted PVSCs. Thus, a very promising efficiency of 18.29% with negligible hysteresis and good device stability can be delivered by PASQ-IDT-based inverted PVSCs in the absence of dopants, outperforming the PEDOT:PSS-based control devices (16.14%) and most dopant-free HTMs reported so far.

A new red fluorophore with aggregation enhanced emission by an unexpected “One-step” protocol

In this work, a triphenylamine-benzothiadiazole-based new fluorophore is obtained from a facile “one-step” protocol. A possible reduction mechanism is proposed, and an amine containing α-H plays a key role in the reduction reaction. The resultant product A1H2 exhibits bright red emission in solid state, with an absolute quantum yield of 44.5%. Aggregation induced emission enhancement of A1H2 is also observed with the increased water fraction in THF-H2O mixture. The nanoparticles of A1H2 reveal good stability and biocompatibility, which are successfully applied in cellular cytoplasm imaging.

Electron extraction layer based on diketopyrrolopyrrole/isoindigo to improve the efficiency of inverted perovskite solar cells

Diketopyrrolopyrrole (DPP) and isoindigo (ISO) moieties have been widely studied in organic optoelectronic materials, while they have been rarely explored as electron transporting materials in perovskite solar cells (PSCs). In this paper, two organic molecules, tetraphenylethylene-diketopyrrolopyrrole (TPE-DPP4) and tetraphenylethylene-isoindigo (TPE-ISO4), were synthesized and successfully used in inverted PSCs. Cyclic voltammetry measurement revealed the matched energy levels of the TPE-based interlayers with perovskite materials. Steady-state photoluminescence (PL) spectra, time-resolved PL decay results and electrochemical impedance spectroscopy (EIS) indicate the enhanced electron extraction and electron-transporting ability after introducing the TPE-DPP4/TPE-ISO4-based interlayer in PSCs. As a result, devices with TPE-DPP4 and TPE-ISO4 interlayers exhibit high power conversion efficiencies (PCEs) of 18.44% and 18.19%, respectively, and notably, the FF values are as high as 80%. The standard device without an interlayer was also measured, showing an inferior PCE of 16.87%. Therefore, TPE-DPP4 and TPE-ISO4 can work as efficient interfacial materials for improving electron transfer, and finally for enhancing the photovoltaic performance in inverted PSCs. As far as we know, this is the first report on the DPP/ISO-based interfacial layer in perovskite solar cells. The results in this work also demonstrate the great potential of DPP or ISO-based n-type materials for application in PSCs.

Regulating the electron transporting properties of indacenodithiophene derivatives for perovskite solar cells with PCEs up to 19.51

Indacenodithiophene-based multi-fused aromatic structures have been largely developed as non-fullerene acceptors for organic solar cells and gained great successes. However, they are less explored as electron transporting materials for perovskite solar cells, despite their compatible energy levels and good electron mobilities. In this work, three n-type non-fullerene acceptors are applied as electron transporting materials in inverted perovskite solar cells (PSCs). All three compounds are of a rigid ladder-type structure with different conjugation lengths of the central multi-fused ring and end-capped with 2-(6-oxo-5,6-dihydro-4H-cyclopenta[c]thiophen-4-ylidene)malononitrile (CPTCN). Consequently, IDTCN, IDT6CN and ITCPTC with five, six and seven fused-rings are obtained. The longest conjugation length in ITCPTC leads to the enhanced electron mobility, and electron extraction and electron transporting ability. In addition, the ITCPTC molecule shows a predominant “face-on” orientation in neat films, which is favorable for charge transport in PSCs. As a result, inverted PSCs using the ITCPTC ETL deliver a champion efficiency of 17.42%, while the devices with IDT6CN and IDTCN exhibit a lower efficiency of 15.56% and 13.86%. Moreover, the non-fullerene acceptors also perform well when applied as interfacial materials in PSCs; ITCPTC delivers a remarkable efficiency of 19.51%, with a FF value as high as 82%. This work reveals the great potential of indacenodithiophene-based non-fullerene acceptors as efficient electron transporting materials for PSCs. The investigation towards the structure–electron transporting property relationship could provide insights for future design of efficient ETMs for inverted PSCs.