Kasparas Rakstys

Foldable Hole-Transporting Materials for Merging Electronic States between Defective and Perfect Perovskite Sites

Keith Gregory Brooks, Paul Joseph Dyson, Ruiyuan Hu, Hiroyuki Kanda, Mohammad Khaja Nazeeruddin, Kasparas Rakstys, Jianxing Xia, Yi Zhang

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 (ABX(3)), are undertaken. Herein, foldable hole-transporting materials (HTMs) are developed, and they extend the wavefunctions of A-site cations of perovskite, which, as hybridized electronic states, link the trap states (defective site) and valence band edge (perfect site) between the naturally defective and perfect sites of the perovskite surface, finally converting the discrete trap states of the perovskite as the continuous valence band to reduce trap recombination. Tailoring the foldability of the HTMs tunes the wavefunctions between defective and perfect surface sites, allowing the power conversion efficiency of a small cell to reach 23.22% and that of a mini-module (6.5 x 7 cm, active area = 30.24 cm(2)) to reach as high as 21.71% with a fill factor of 81%, the highest value reported for non-spiro-OMeTAD-based perovskite solar modules.

WILEY-V C H VERLAG GMBH2023

Transparent Liquid Crystal Hole-Transporting Material for Stable Perovskite Solar Cells

Hiroyuki Kanda, Mohammad Khaja Nazeeruddin, Kasparas Rakstys, Jianxing Xia

Hexakis(hexyloxy)triphenylene (HAT6) discotic liquid crystal is employed as a transparent hole-transporting material (HTM) for perovskite solar cells (PSCs) and a power conversion efficiency (PCE) of 15.7% is obtained, which is the highest using HAT6 type of HTMs. Despite lower PCE than spiro-OMeTAD-based devices (20.3%), the PSCs based on HAT6 exhibit much higher ambient and thermal stability. A fused polyaromatic core with six alkyl chains leads to high hydrophobicity, and the pi-stacked molecular columns of the HAT6 shield the bis(trifluoromethane)sulfonamide lithium salt dopant migration into the perovskite absorber. The PSCs (under N-2 condition) exhibit superior stability compared to the devices employing spiro-OMeTAD, retaining nearly 92% of their initial efficiency after 1200 h operation. Under ambient conditions, HAT6-based hole-transportation layer devices retain 93% of the initial efficiency for 690 h. Under continuous thermal stress of 85 degrees C, the devices based on HAT6 retain 95% of the initial PCE. The results demonstrate the time applicability of liquid crystal for stable PSCs fabrication.

WILEY-V C H VERLAG GMBH2023

Passivating Defects of Perovskite Solar Cells with Functional Donor-Acceptor-Donor Type Hole Transporting Materials

Mohammad Khaja Nazeeruddin, Kasparas Rakstys, Jianxing Xia, Yi Zhang

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 only carrier transportation but also defects passivation via Pb-N interactions. The highest power conversion efficiency of over 22% is achieved on cells based on V1359, which is higher than that of spiro-OMeTAD under identical conditions. This st shows that HTMs prepared via simplified synthetic routes are not only a low-cost alternative to spiro-OMeTAD but also outperform in efficiency and stability state-of-art materials obtained via expensive cross-coupling methods.

WILEY-V C H VERLAG GMBH2022

Zn(II) and Cu(II) tetrakis(diarylamine)phthalocyanines as hole-transporting materials for perovskite solar cells

Cansu Igci, Hiroyuki Kanda, Nadja Isabelle Desiree Klipfel, Wei Li, Mohammad Khaja Nazeeruddin, Kasparas Rakstys, Jianxing Xia

Finding new hole-transporting materials (HTMs) suitable for replacing the state-of-the-art spiro-OMe-TAD is still challenging. In this work, newly synthesized diarylamine-substituted metal phthalocyanines (MPcs, M 1/4 Zn(II) or Cu(II)) functionalized with either linear or branched alkoxy chains are evaluated as HTMs in perovskite solar cells. Both the nature of the alkoxy chains and that of the coordinated metal species were found to influence the functional properties of the new MPcs. In particular, devices based on a ZnPc featuring four n-butoxy side chains exhibited the highest power conversion efficiencies (PCEs). A PCE of 20.00% was reached for triple cation perovskite devices, and a PCE up to 20.18% could be achieved for double cation devices. (C) 2022 The Authors. Published by Elsevier Ltd.

ELSEVIER SCI LTD2022

Branched Methoxydiphenylamine-Substituted Carbazole Derivatives for Efficient Perovskite Solar Cells: Bigger Is Not Always Better

Hiroyuki Kanda, Mohammad Khaja Nazeeruddin, Kasparas Rakstys, Jianxing Xia, Yi Zhang

A set of novel branched molecules bearing a different number of 3,6-bis(4,4'-dimethoxydiphenylamino)carbazole-based (CzOMeDPA) 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 number of Cz-OMeDPA moieties and the nature of the linking aliphatic chain. The isolated compounds possess sufficient thermal stability and are amorphous having high glass-transition temperatures (>120 degrees C) minimizing the risk of direct layer crystallization. The highest hole-drift mobility of mu(0) = 3.1 x 10(-5) cm(2) V-1 s(-1) is comparable to that of the reference standard spiro-OMeTAD (4.1 x 10(-5) cm(2) V-1 s(-1)) under identical conditions. Finally, PSCs employing two new HTMs (2CzOMeDPA and 3Cz-OMeDPA-OH) bearing two and three substituted carbazole chromophores, linked by an aliphatic chain, show a performance of around 20%, which is on par with devices using spiroOMeTAD and demonstrates slightly enhanced device stability.

AMER CHEMICAL SOC2021

Cut from the Same Cloth: Enamine-Derived Spirobifluorenes as Hole Transporters for Perovskite Solar Cells

Bin Ding, Paul Joseph Dyson, Cansu Igci, Mohammad Khaja Nazeeruddin, Kasparas Rakstys, Albertus Adrian Sutanto

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 charges from the light-absorbing perovskite layer and carry them to the electrode. Here, we report spirobifluorene-based HTMs with finely tuned energy levels, high glass-transition temperature, and excellent charge mobility and conductivity enabled by molecularly engineered enamine arms. HTMs are synthesized using simple condensation chemistry, which does not require costly catalysts, inert reaction conditions, and time-consuming product purification procedures. Enamine-derived HTMs allow the fabrication of PSCs reaching a maximum PCE of 19.2% and stability comparable to spiro-OMeTAD. This work demonstrates that simple enamine condensation reactions could be used as a universal path to obtain HTMs for highly efficient and stable PSCs.

AMER CHEMICAL SOC2021

Dopant‐Free Hole Transport Materials Afford Efficient and Stable Inorganic Perovskite Solar Cells and Modules

Bin Ding, Yong Ding, Paul Joseph Dyson, Cansu Igci, Hiroyuki Kanda, Cheng Liu, Mohammad Khaja Nazeeruddin, Kasparas Rakstys, Olga Syzgantseva, Yi Yang

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. The suitable optoelectronic properties and energy-level alignment endow CI-TTIN-2F with excellent charge collection properties. Moreover, CI-TTIN-2F provides multisite defect-healing effects on the defective sites of CsPbI3 surface. 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. Inorganic perovskite solar modules were also fabricated that exhibiting an efficiency of 11.0 % with a record area of 27 cm2. This work confirms that using efficient dopant-free HTMs is an attractive strategy to stabilize inorganic PSCs for their future scale-up.

2021

Fluorene-based enamines as low-cost and dopant-free hole transporting materials for high performance and stable perovskite solar cells

Mohammad Khaja Nazeeruddin, Kasparas Rakstys, Albertus Adrian Sutanto

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 are synthesized via cross-coupling reactions which require expensive catalysts, inert reaction conditions and time-consuming sophisticated product purification. In a quest to employ cost-effective chemistry to combine the building blocks, we explore enamine-based small molecules that can be synthesized in a simple condensation reaction from commercially available materials leading to an estimated material cost of a few euros per gram. The synthesized fluorene-based enamines exhibit a very high hole mobility up to 3.3 x 10(-4) cm(2) V-1 s(-1) and enable the fabrication of perovskite solar cells with a maximum power conversion efficiency of 19.3% in a doped configuration and 17.1% without doping. In addition, both PSC systems demonstrate superior long-term stability compared to spiro-OMeTAD. This work shows that hole transporting materials prepared via a simple condensation protocol have the potential to compete in terms of performance with materials obtained via expensive cross-coupling methods at a fraction of their cost and deliver exceptional stability of the final device. This work provides a design strategy for the further development of novel, low-cost semiconductors.

ROYAL SOC CHEMISTRY2021

Carbazole-Terminated Isomeric Hole-Transporting Materials for Perovskite Solar Cells

Hiroyuki Kanda, Mohammad Khaja Nazeeruddin, Sanghyun Paek, Kasparas Rakstys

A set of novel hole-transporting materials (HTMs) based on pi-extension through carbazole units was designed and synthesized via a facile synthetic procedure. The impact of isomeric structural linking on their optical, thermal, electrophysical, and photovoltaic properties was thoroughly investigated by combining the experimental and simulation methods. Ionization energies of HTMs were measured and found to be suitable for a triple-cation perovskite active layer ensuring efficient hole injection. New materials were successfully applied in perovskite solar cells, which yielded a promising efficiency of up to almost 18% under standard 100 mW cm(-2) global AM1.5G illumination and showed a better stability tendency outperforming that of 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene. This work provides guidance for the molecular design strategy of effective holeconducting materials for perovskite photovoltaics and similar electronic devices.

AMER CHEMICAL SOC2020