Kasparas Rakstys

Kaunas University of Technology · Department of Organic Chemistry

Organic halide salt passivation is considered to be an essential strategy to reduce defects in state-of-the-art perovskite solar cells (PSCs). This strategy, however, suffers from the inevitable formation of in-plane favored two-dimensional (2D) perovskite layers with impaired charge transport, especially under thermal conditions, impeding photovol...

Efficient and stable perovskite solar cells with a simple active layer are desirable for manufacturing. Three-dimensional perovskite solar cells are most efficient but need to have improved environmental stability. Inclusion of larger ammonium salts has led to a trade-off between improved stability and efficiency, which is attributed to the perovsk...

Four center symmetrical star-shaped hole transporting materials (HTMs) comprising planar triazatruxene core and electron-rich methoxy-engineered side arms have been synthesized and successfully employed in compositive perovskite solar cells. These HTMs are obtained from relatively cheap starting materials by adopting facile preparation procedure, w...

The 4,4’-dimethoxydiphenylamine-substituted 9,9'-bifluorenylidene (KR216) hole transporting material has been synthesized using a straightforward two-step procedure from commercially available and inexpensive starting reagents, mimicking the synthetically challenging 9,9'-spirobifluorene moiety of the well-studied spiro-OMeTAD. A power conversion e...

Through judicious molecular engineering, novel dopant-free star-shaped D–π–A type hole transporting materials coded KR355, KR321, and KR353 were systematically designed, synthesized and characterized. KR321 has been revealed to form a particular face-on organization on perovskite films favoring vertical charge carrier transport and for the first ti...

Molecular hole-transporting materials (HTMs) having triphenylethylene central core were designed, synthesized, and employed in perovskite solar cell (PSC) devices. The synthesized HTM derivatives were obtained in a two- or three-step synthetic procedure, and their characteristics were analyzed by various thermoanalytical, optical, photophysical, an...

A novel 9,9′-spirobifluorene derivative bearing thermally cross-linkable vinyl groups (V1382) was developed as a hole-transporting material for perovskite solar cells (PSCs). After thermal cross-linking, a smooth and solvent-resistant three-dimensional (3D) polymeric network is formed such that orthogonal solvents are no longer needed to process su...

In this work, a series of passivating salts for perovskite solar cells (PSCs) based on the ortho-methylammonium iodide functional units are molecularly engineered to study the steric hindrance driven passivation effect. The incorporation of the fluorine atoms in passivating agents has been found to be beneficial not only for maximized defects passi...

Perovskite solar cells are among the most promising photovoltaic technologies in academia and have the potential to become commercially available in the near future. However, there are still a few unresolved issues regarding device lifetime and fabrication cost of perovskite solar cells in order to be competitive with existing technologies. Herein,...

A group of small-molecule hole-transporting materials (HTMs) that are based on fluorenylidene fragments were synthesized and tested in perovskite solar cells (PSCs). The investigated compounds were synthesized by a facile two-step synthesis, and their properties were measured using thermoanalytical, optoelectronic, and photovoltaic methods. The cha...

Defective and perfect sites naturally exist within electronic semiconductors, and considerable efforts to reduce defects to improve the performance of electronic devices, especially in hybrid organic-inorganic perovskites (ABX3 ), have been undertaken. Herein, foldable hole transporting materials (HTMs) were developed, and extend the wavefunctions...

Hexakis(hexyloxy)triphenylene (HAT6) discotic liquid crystal (DLC) is employed as transparent hole transporting material (HTM) for perovskite solar cells (PSCs) and obtained a power conversion efficiency (PCE) of 15.7%, which is the highest using HAT6 type of HTMs. Despite lower PCE than spiro‐OMeTAD based devices (20.3%), the PSCs based on HAT6 ex...

Hole‐transporting materials (HTMs) based on the 10H, 10′H‐9,9′‐spirobi [acridine] core (BSA50 and BSA51) were synthesized, and their electronic properties were explored. Experimental and theoretical studies show that the presence of rigid 3,6‐dimethoxy‐9H‐carbazole moieties in BSA 50 brings about improved hole mobility and higher work function comp...

In this study, a series of donor–acceptor–donor (D‐A‐D) type small molecules based on the fluorene and diphenylethenyl enamine units, which are distinguished by different acceptors, as holetransporting materials (HTMs) for perovskite solar cells is presented. The incorporation of the malononitrile acceptor units is found to be beneficial for not on...

Two hole‐transporting materials (HTMs) based on the 10 H , 10'H‐9,9'‐spirobi [acridine] core ( BSA50 and BSA51 ) were synthesized, and their electronic and hole transportation properties were explored. Experimental and theoretical studies show that the presence of rigid 3,6‐dimethoxy‐9H‐carbazole moieties in BSA 50 brings about improved hole mobili...

Perovskite light emitting diodes (PeLEDs) have emerged as promising candidates for applications requiring visible and near-infrared emission. Lead-based quasi-2D perovskite materials are commonly employed as an emissive layer for PeLEDs as they promote radiative emission via spatially confining excitons and funnelling of charge carriers. Designing...

Stabilizing the high‐performing perovskite solar cells (PSCs) with low‐cost and simply affordable hole‐transporting materials (HTMs) has been identified as an ongoing ambitious challenge. Herein, a series of enamine‐based HTMs having different central heteroatom (C, N, O, and S) and a number of enamine branches was designed and synthesized. The imp...

Finding new hole-transporting materials (HTMs) suitable for replacing the state-of-the-art spiro-OMeTAD is still challenging. In this work, newly synthesized diarylamine-substituted metal phthalocyanines (MPcs, M = Zn(II) or Cu(II)) functionalized with either linear or branched alkoxy chains are evaluated as HTMs in perovskite solar cells. Both the...

Triarylamine end-capped-functionalized arylene-imidazole derivatives were synthesized from readily accessible, inexpensive precursors and employed as hole transporting materials (HTMs) in perovskite solar cells (PSCs). All the HTMs displayed high thermal decomposition temperatures (>410 °C), which is beneficial for realizing stable PSC devices. In...

Hybrid lead halide perovskite solar cells (PSCs) have emerged as potential competitors to silicon-based solar cells with an unprecedented increase in power conversion efficiency (PCE), nearing the breakthrough point toward commercialization. However, for hole-transporting materials, it is generally acknowledged that complex structures often create...

Hybrid lead halide perovskite solar cells (PSCs) have emerged as potential competitors to silicon‐based solar cells with an unprecedented increase in power conversion efficiency (PCE), nearing the breakthrough point toward commercialization. However, for hole‐transporting materials, it is generally acknowledged that complex structures often create...

Three benzodipyrrole (BDP)-based organic small molecules with substituted 4-methoxyphenyl (CB-1), 3-fluorophenyl (CB-2), and 3-trifluoromethylphenyl (CB-3) are designed, synthesized, and used as a hole-transporting material (HTM) for perovskite solar cells (PSCs). The electrochemical, optical, thermal, electronic, and optoelectronic properties of t...

A set of novel branched molecules bearing a different number of 3,6-bis(4,4′-dimethoxydiphenylamino)carbazole-based (Cz-OMeDPA) periphery arms linked together by aliphatic chains have been developed, and their performance has been tested in perovskite solar cells (PSCs). Electrical and photovoltaic properties have been evaluated with respect to the...

The emerging CsPbI3 perovskites are highly efficient and thermally stable materials for wide‐band gap perovskite solar cells (PSCs), but the doped hole transport materials (HTMs) accelerate the undesirable phase transition of CsPbI3 in ambient. Herein, a dopant‐free D‐π‐A type HTM named CI‐TTIN‐2F has been developed which overcomes this problem. Th...

To attain commercial viability, perovskite solar cells (PSCs) have to be reasonably priced, highly efficient, and stable for a long period of time. Although a new record of a certified power conversion efficiency (PCE) value over 25% was achieved, PSC performance is limited by the lack of hole-transporting materials (HTMs), which extract positive c...

Organic halide salt passivation is considered to be an essential strategy to reduce defects in state-of-the-art perovskite solar cells (PSCs). This strategy, however, suffers from the inevitable formation of in-plane favored two-dimensional (2D) perovskite layers with impaired charge transport, especially under thermal conditions, impeding photovol...

A dopant-free D-π-A type HTM named CI-TTIN-2F has been developed which showing excellent charge collection properties and multisite defect-healing effects. All-inorganic CsPbI3 PSCs with CI-TTIN-2F HTM feature high efficiencies up to 15.9 %, along with 86 % efficiency retention after 1000 h under ambient conditions. All-inorganic perovskite solar m...

Triarylamine‐substituted bithiophene (BT‐4D), terthiophene (TT‐4D), and quarterthiophene (QT‐4D) small molecules are synthesized and used as low‐cost hole‐transporting materials (HTMs) for perovskite solar cells (PSCs). The optoelectronic, electrochemical, and thermal properties of the compounds are investigated systematically. The BT‐4D, TT‐4D, an...

Two structural isomers of carbazole decorated with triarylamine have been designed and synthesized with a facile synthetic procedure. The impact of triarylamine substitution on the isomeric structural linkage of carbazole on the optical, thermal, electrochemical, and photovoltaic properties has been extensively studied by combining experimental and...

The power conversion efficiency of perovskite solar cells is approaching the Shockley–Queisser limit, and therefore this technology is next to the commercialization stage. Inexpensive and stable hole transporting materials are highly desirable for the successful scale-up. Most high performing devices generally employ expensive hole conductors that...

Three donor–π‐bridge–acceptor (D–π–A) type organic small molecules coded CI‐B1, CI‐B2 and CI‐B3 are designed, synthesized and used as dopant‐free hole transporting materials (HTMs) for perovskite solar cells (PSCs). The strong electron‐donating triazatruxene central core (D), terthiophene conjugated arms (π) and three different strong electron‐acce...

A set of novel hole-transporting materials (HTMs) based on π-extension through the carbazole units were designed and synthesized via a facile synthetic procedure. The impact of isomeric structural linking on their optical, thermal, electrophysical, and photovoltaic properties were thoroughly investigated combining experimental and simulation method...

Insoluble glycol-derivatized poly(1,4-phenylenevinylene)s (PPVs) have been prepared by in situ thermal conversion of solution-processable xanthate precursor polymers and used as interlayers in inverted perovskite solar cells. The insolubility of the PPVs enabled the perovskite active layer to be deposited on top without dissolution, and the glycol...

Metallophthalocyanines (MPcs) are currently emerging as alternative hole-transporting materials (HTMs) in perovskite solar cells (PSCs). However, the lack of systematic structure/photovoltaic properties investigations still hampers the rational design of MPcs that might act as efficient HTMs for PSCs. We designed and tested a series of symmetric MP...

The invention discloses a polymerizable triazatruxene-based compound of formula (I), an optoelectronic and/or photoelectrochemical device comprising said compound of formula (I) as hole transporting material in hole transport layer under the form of a polymer, and a method of fabrication thereof.

In the last decade, perovskite solar cells are considered a promising and burgeoning technology for solar energy conversion with power conversion efficiency, currently exceeding 24%. However, although perovskite solar cells have reached high power conversion efficiency, there are still several challenges limiting the industrial realization. The act...

A cross-linkable triazatruxene that leads to insoluble films upon thermal annealing at temperatures compatible with flexible substrates is presented. The films were used as the hole transporting and electron blocking layer in partially solution processed phosphorescent organic light-emitting diodes, reaching power conversion efficiencies of 24 lm W...

Hole transporting materials (HTMs), used in perovskite solar cells, are routinely doped with several additives. This work shows the reaction of HTM with a tert-butylpyridine additive, which has a negative impact on device performance.

In this work, for the first time, reactive radical-cation species present in hole-transporting materials were shown to react with tert-butylpyridine additive, routinely used in hole transporting layer composition. As a result, new pyridinated products were isolated and characterized by NMR and MS analysis. Additionally, their optical and photophysi...

The present invention relates to a compound of formula (I) based on enamine derivatives and used as organic hole conductors or hole transporting material in an optoelectronic or photoelectrochemical device. The present invention relates to the hole transporting compounds based on enamine derivatives for efficiency perovskite or dye sensitized solar...

A series of new branched hole transporting materials (HTMs) containing two diphenylamine-substituted carbazole fragments linked by a nonconjugated methylenebenzene unit is synthesized and tested in perovskite solar cells. Synthesis of the investigated materials is performed by a simple two-step synthetic procedure providing a target product in high...

The dispiro-oxepine/dispiro-thiapine derivatives for optoelectronic semiconductors is a compound based on a structure having a functionalized dispiro compound of formula (Ia) or (Ib) with the core unit being a seven-membered heterocycle oxepine or thiapine, the derivative being formed by combining (Ia) or (Ib): with two moities selected from K1 and...

Molecularly engineered novel dopant-free hole-transporting materials for perovskite solar cells (PSCs) combined with mixed-perovskite (FAPbI3 )0.85 (MAPbBr3 )0.15 (MA: CH3 NH3(+) , FA: NH=CHNH3(+) ) that exhibit an excellent power conversion efficiency of 18.9% under AM 1.5 conditions are investigated. The mobilities of FA-CN, and TPA-CN are determ...

The synthesis, characterization and photovoltaic performance of series of novel molecular hole transporting materials (HTMs) based on bistricyclic aromatic enes (BAEs) are presented. The new derivatives have been obtained following the simple and straightforward two-step procedure from inexpensive starting reagents mimicking the synthetically chall...

Dimethoxydiphenylamine-substituted dispiro-oxepine derivative 2,2',7,7'-tetrakis-(N,N'-di-4-methoxyphenylamine)dispiro-[fluorene-9,4'-dithieno[3,2-c:2',3'-e]oxepine-6',9''-fluorene] (DDOF) has been designed and synthesized using a facile synthetic route. The novel hole transporting material (HTM) was fully characterized and tested in perovskite sol...

Amino donor groups-substituted zinc(II) phthalocyanines (ZnPcs) BI25, BL07 and BL08 were obtained via cyclotetramerization of suitable phthalonitriles that were synthesized by Pd catalyzed amination reaction between 4-iodophthalonitrile and a selected secondary amine. The BI25, BL07 and BL08 ZnPcs were characterized using spectroscopic and electroc...

Molecularly engineered weakly conjugated hybrid porphyrin systems are presented as efficient sensitizers for solid-state dye-sensitized solar cells. By incorporating the quinolizino acridine and triazatruxene based unit as the secondary light-harvester as well as electron-donating group at the meso-position of the porphyrin core, the power conversi...

Donor-π-Bridge-Donor type oligomers (D-π-D) have been studied intensively as active materials for organic optoelectronic devices. In this study, we introduce three new D-π-D type organic semiconductors incorporating thiophene or thienothiophene with two electron-rich TPA units, which can be synthesized easily from commercially available materials....

The 4,4′-dimethoxydiphenylamine-substituted 9,9′-bifluorenylidene (KR216) hole transporting material has been synthesized using a straightforward two-step procedure from commercially available and inexpensive starting reagents, mimicking the synthetically challenging 9,9′-spirobifluorene moiety of the well-studied spiro-OMeTAD. A power conversion e...

The small-molecule hole transporting materials based on indolocarbazole core were synthesized and incorporated into perovskite solar cells, which displayed a power conversion efficiency of up to 15.24%. The investigated hole transporting materials were synthesized in three steps from commercially available and relatively inexpensive starting materi...

This review presents an overview of the dedicated research directions of the Group for Molecular Engineering of Functional Materials (GMF). This includes molecular engineering aspects of sensitizers constructed from ruthenium complexes, organic molecules, porphyrins and phthalocyanines. Manipulation of organometal trihalide perovskites, and charge...

Triazatruxene core based hole transporting materials (HTMs), HMDI (5,10,15-trihexyl-3,8,13-trimethoxy-10,15-dihydro-5H-diindolo[3,2-a:3',2'-c]carbazole) and HPDI (5,10,15-tris(4-(hexyloxy)phenyl)-10,15-dihydro-5H-diindolo[3,2-a:3',2'-c]carbazole) were synthesized and exploited in perovskite based solar cells. The energy levels of star-shaped HMDI a...

This review presents an overview of the dedicated research directions of the Group for Molecular Engineering of Functional Materials (GMF). This includes molecular engineering aspects of sensitizers constructed from ruthenium complexes, organic molecules, porphyrins and phthalocyanines. Manipulation of organometal trihalide perovskites, and charge...

The present invention relates to an electrode layer comprising a porous film made of oxide semiconductor fine particles sensitized with a methine dye having a counter anion capable of absorbing electromagnetic radiation having a wavelength in the range of from 400 nm to 1000 nm. Moreover the present invention relates to a photoelectric conversion d...

A series of donor–chromophore–anchor (D–C–A) sensitizers comprising the diketopyrrolopyrrole (DPP) chromophore were synthesized and tested in both I3−/I− and Co[(bpy)]3+/2+ redox shuttle DSC devices. The dye series was strategically designed to elucidate structure–property relationships, concerning overall performance and compatibility with these t...

The paradigm shift in dye sensitized solar cells (DSCs) - towards donor- π bridge-acceptor (D-π-A) dyes - increases the performances of DSCs and challenges established design principles. Framed by this shifting landscape, a series of four diketopyrrolopyrrole (DPP)-based sensitizers utilizing the donor-chromophore-anchor (D-C-A) motif were investig...

A novel, asymmetric DPP bridge/core was synthesized and tested in DSC devices. By desymmetrising the DPP core/bridge, a remarkable IPCE of >80% and a maximum power conversion efficiency of 7.7% were achieved. With the use of a wide-bandgap co-sensitizer, 8.6% PCE was realized under standard AM1.5G sunlight.

Four D-π-A sensitizers comprising a thienyl-diketopyrrolopyrrole (ThDPP) bridge were synthesized and tested in iodide/triiodide liquid electrolyte DSC devices. The dye series was strategically designed to develop a structure-property relationship. The best performing sensitizer utilized a phenyl-based anchor and triphenylamine donor (η = 5.03%).