Halogen Bonded Hole Transport Material Suppresses Charge Recombination and Enhances Stability of Perovskite Solar Cells

Interfaces play a crucial role in determining perovskite solar cells, PSCs performance and stability. It is therefore of great importance to constantly work toward improving their design. This study shows the advantages of using a hole transport material HTM that can anchor to the perovskite surface through halogen bonding XB . A halo functional HTM PFI is compared to a reference HTM PF , identical in optoelectronic properties and chemical structure but lacking the ability to form XB. The interaction between PFI and perovskite is supported by simulations and experiments. XB allows the HTM to create an ordered and homogenous layer on the perovskite surface, thus improving the perovskite HTM interface and its energy level alignment. Thanks to the compact and ordered interface, PFI displays increased resistance to solvent exposure compared to its not interacting counterpart. Moreover, PFI devices show suppressed nonradiative recombination and reduced hysteresis, with a Voc enhancement of bigger equal as 20 mV and a remarkable stability, retaining more than 90 efficiency after 550 h of continuous maximum power point tracking. This work highlights the potential that XB can bring to the context of PSCs, paving the way for a new halo functional design strategy for charge transport layers, which tackles the challenges of charge transport and interface improvement simultaneousl

Low-Cost Phenothiazine- and Pyrene-Based Hole-Transporting Materials for Halide Perovskite Solar Cells

Organic-inorganic halide perovskite solar cells (PSCs) show great potential for energy applications due to their excellent power conversion efficiency that dramatically increased from 3.8 % to over 25% in just a decade of research. The performance of PSCs is strongly influenced by the charge-transporting (electron and hole) layers. Currently, most of the high-performing PSCs use 2,2’,7,7’-tetrakis-(N,N’-di-p- methoxyphenylamine)-9,9’-spirobifluorene) (Spiro-OMeTAD) or polytriarylamine (PTAA) as hole-transporting materials (HTMs). However, Spiro-OMeTAD and PTAA suffer from several drawbacks, such as extremely high cost, difficult and multistep synthesis and purification, and low hole mobility and conductivity, thus requiring the use of additional chemical dopants. The addition of dopants not only decreases the device stability but also increases the complexity of device fabrication. Considering all the above-mentioned drawbacks it is highly desirable to design alternative HTMs to simplify the fabrication of PSCs and ensure their industrial-scale application. This work investigates the molecular design, synthesis, and application of phenothiazine- and pyrene-core organic small molecule-based HTMs for efficient and stable PSCs. Ullman and Suzuki coupling reactions, as well as simple condensation reactions, were used to synthesize the HTMs. The optical and electrochemical properties of the HTMs were tuned by the introduction of electron donor and acceptor groups to the parent materials. The newly synthesized HTMs exhibited excellent interactions with the perovskite surface. The azomethine HTMs led to PSCs with a power conversion efficiency of up to 14% and with high stability, environmentally friendly synthesis, and very low cost (~ 10$/g). The optical and electrochemical properties of the pyrene-core HTMs, as well as the performance of corresponding PSCs, were tuned by an effective fluorination strategy. We believe that the molecular designs presented in this work will provide useful know-how to significantly enhance the stability and the performance of PSCs, thus bringing them closer to commercialization. In particular, our focus has been on developing material with cost-efficient synthesis and minimal environmental impact

Low-Cost Phenothiazine- and Pyrene-Based Hole-Transporting Materials for Halide Perovskite Solar Cells

Organic-inorganic halide perovskite solar cells (PSCs) show great potential for energy applications due to their excellent power conversion efficiency that dramatically increased from 3.8 % to over 25% in just a decade of research. The performance of PSCs is strongly influenced by the charge-transporting (electron and hole) layers. Currently, most of the high-performing PSCs use 2,2’,7,7’-tetrakis-(N,N’-di-p- methoxyphenylamine)-9,9’-spirobifluorene) (Spiro-OMeTAD) or polytriarylamine (PTAA) as hole-transporting materials (HTMs). However, Spiro-OMeTAD and PTAA suffer from several drawbacks, such as extremely high cost, difficult and multistep synthesis and purification, and low hole mobility and conductivity, thus requiring the use of additional chemical dopants. The addition of dopants not only decreases the device stability but also increases the complexity of device fabrication. Considering all the above-mentioned drawbacks it is highly desirable to design alternative HTMs to simplify the fabrication of PSCs and ensure their industrial-scale application. This work investigates the molecular design, synthesis, and application of phenothiazine- and pyrene-core organic small molecule-based HTMs for efficient and stable PSCs. Ullman and Suzuki coupling reactions, as well as simple condensation reactions, were used to synthesize the HTMs. The optical and electrochemical properties of the HTMs were tuned by the introduction of electron donor and acceptor groups to the parent materials. The newly synthesized HTMs exhibited excellent interactions with the perovskite surface. The azomethine HTMs led to PSCs with a power conversion efficiency of up to 14% and with high stability, environmentally friendly synthesis, and very low cost (~ 10$/g). The optical and electrochemical properties of the pyrene-core HTMs, as well as the performance of corresponding PSCs, were tuned by an effective fluorination strategy. We believe that the molecular designs presented in this work will provide useful know-how to significantly enhance the stability and the performance of PSCs, thus bringing them closer to commercialization. In particular, our focus has been on developing material with cost-efficient synthesis and minimal environmental impact

Hole-Transporting Materials for Printable Perovskite Solar Cells

Perovskite solar cells (PSCs) represent undoubtedly the most significant breakthrough in photovoltaic technology since the 1970s, with an increase in their power conversion efficiency from less than 5% to over 22% in just a few years. Hole-transporting materials (HTMs) are an essential building block of PSC architectures. Currently, 2,2’,7,7’-tetrakis-(N,N’-di-p-methoxyphenylamine)-9,9’-spirobifluorene), better known as spiro-OMeTAD, is the most widely-used HTM to obtain high-efficiency devices. However, it is a tremendously expensive material with mediocre hole carrier mobility. To ensure wide-scale application of PSC-based technologies, alternative HTMs are being proposed. Solution-processable HTMs are crucial to develop inexpensive, high-throughput and printable large-area PSCs. In this review, we present the most recent advances in the design and development of different types of HTMs, with a particular focus on mesoscopic PSCs. Finally, we outline possible future research directions for further optimization of the HTMs to achieve low-cost, stable and large-area PSCs.publishedVersionPeer reviewe

Multicomponent Petasis-borono Mannich Preparation of Alkylaminophenols and Antimicrobial Activity Studies

In this work we report the antibacterial activity of alkylaminophenols. A series of such compounds was prepared by a multicomponent Petasis-borono Mannich reaction starting from salicylaldehyde and its derivatives. The obtained compounds were tested against a large panel of microorganisms, Gram-positive and Gram-negative bacteria, and a yeast. Among the several tertiary amine derivatives tested, indoline-derived aminophenols containing a nitro group at the para-phenol position showed considerable activity against bacteria tested with minimal inhibitory concentrations as low as 1.36 μm against Staphyloccocus aureus and Mycobacterium smegmatis. Cytotoxicity of the new para-nitrophenol derivatives was observed only at concentrations much higher than those required for antibacterial activity.acceptedVersionPeer reviewe

Protonation-induced fluorescence modulation of carbazole-based emitters

The development of purely organic fluorescence emitters is of great importance for their low cost and high performance. Responding to this demand, carbazole is a promising emitter due to its extensive freedom for functionalisation, high thermal and chemical stability, as well as low cost. Herein, the effect of protonation on the fluorescence of various pyridine-functionalised carbazole-based bipolar host materials was studied both in solution and in the solid-state. The restriction of intramolecular rotation of the molecules upon protonation of the pyridyl-moiety together with easier planarization of the protonated acceptor and the donor moieties and relocalisation of the LUMO orbital on the protonated species was found to increase the fluorescence quantum yield from 16% to 80%. Additionally, in the solid-state, the J-type packing of the molecules further facilitated the increase in the fluorescence quantum yield from 1% to 49%. In both cases, the pronounced bathochromic spectral shift was observed indicating that the gap between the emissive state and the first triplet state of the molecules was diminished upon protonation. Therefore, implementing this strategy could further boost the development of future emitters.peerReviewe

Crystallisation-enhanced bulk hole mobility in phenothiazine-based organic semiconductors

A series of three novel donor-acceptor systems based on C(3)-malononitrile-substituted phenothiazines was synthesised in good overall yields and their thermal, spectroscopic, and electrochemical properties were characterised. The compounds were prepared through a sequence of Ullmann-coupling, Vilsmeier-Haack formylation and Knoevenagel-condensation, followed by Suzuki-coupling reactions for introduction of aryl substitutents at C(7) position of the phenothiazine. The introduction of a donor unit at the C(7) position exhibited a weak impact on the optical and electrochemical characteristics of the compounds and led to amorphous films with bulk hole mobilities in the typical range reported for phenothiazines, despite the higher charge delocalisation as attested by computational studies. In contrast, highly ordered films were formed when using the C(7)-unsubstituted 3-malononitrile phenothiazine, exhibiting an outstanding mobility of 1 × 10−3 cm2 V−1 s−1, the highest reported for this class of compounds. Computational conformational analysis of the new phenothizanes suggested that free rotation of the substitutents at the C(7) position suppresses the ordering of the system, thereby hampering suitable packing of the new materials needed for high charge carrier mobility.publishedVersionPeer reviewe

Phenothiazine and carbazole substituted pyrene based electroluminescent organic semiconductors for OLED devices

Due to their easy availability, low cost and opportunities for exploiting reactions of bromo substituents, 1,3,6,8-tetrabromopyrene has attracted major attention in the organic electronics community for designing and constructing novel classes of pyrene based organic semiconducting functional materials. In the present work, 1,3,6,8-tetrabromo pyrene was transformed into the corresponding tetrasubstituted carbazole and phenothiazine derivatives using the classical Suzuki coupling reaction. These newly synthesized materials with a carbazole substituent (PY-CA) and a phenothiazine substituent (PY-PH) were characterised thoroughly and were successfully used as an active light-emitting layer in organic light emitting diodes which resulted in blue and green emission with promising device performance. PY-CA exhibited the maximum brightness at around 2500 cd m−2 and the power efficiency of 1.5 lm W−1 while that of PY-PH exhibited 2116 cd m−2 and 0.45 lm W−1 respectively