Understanding Structure-Property Relationships in All-Small-Molecule Solar Cells Incorporating a Fullerene or Nonfullerene Acceptor

Hong, Jisu,Sung, Min Jae,Cha, Hyojung,Park, Chan Eon,Durrant, James R.,An, Tae Kyu,Kim, Yun-Hi,Kwon, Soon-Ki American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.42

<P>To investigate the influence of donor molecule crystallinity on photovoltaic performance in all-small-molecule solar cells, two dithieno[2,3-<I>d</I>:2′,3′-<I>d</I>′]-benzo[1,2-<I>b</I>:4,5-<I>b</I>′]dithiophene (DTBDT)-based small molecules, denoted as DTBDT-Rho and DTBDT-S-Rho and incorporating different side chains, are synthesized and characterized. The photovoltaic properties of solar cells made of these DTBDT-based donor molecules are systemically studied with the [6,6]-phenyl-C<SUB>71</SUB>-butyric acid methyl ester (PC<SUB>71</SUB>BM) fullerene acceptor and the O-IDTBR nonfullerene acceptor to study the aggregation behavior and crystallinity of the donor molecules in both blends. Morphological analyses and a charge carrier dynamics study are carried out simultaneously to derive structure-property relationships and address the requirements of all-small-molecule solar cells. This study reveals exciton decay loss driven by large-scale phase separation of the DTBDT molecules to be a crucial factor limiting photocurrent generation in the all-small-molecule solar cells incorporating O-IDTBR. In the all-small-molecule blends, DTBDT domains with dimensions greater than 100 nm limit the exciton migration to the donor-acceptor interface, whereas blends with PC<SUB>71</SUB>BM exhibit homogeneous phase separation with smaller domains than in the O-IDTBR blends. The significant energy losses in nonfullerene-based devices lead to decreased <I>J</I><SUB>sc</SUB> and fill factor values and unusual decrease in <I>V</I><SUB>oc</SUB> values. These results indicate the modulation of phase separation to be important for improving the photovoltaic performances of all-small-molecule blends. In addition, the enhanced molecular aggregation of DTBDT-S-Rho with the alkylthio side chain leads to higher degrees of phase separation and unfavorable charge transfer, which are mainly responsible for the relatively low photocurrent when using DTBDT-S-Rho compared with that when using DTBDT-Rho. On the other hand, this enhanced molecular aggregation improves the crystallinity of DTBDT-S-Rho and results in its increased hole mobility.</P> [FIG OMISSION]</BR>

Alternative transparent electrodes for Low-cost, flexible small-molecule organic solar cells

김용현,( Lars Muller Meskamp ),( Karl Leo ) 한국공업화학회 2015 한국공업화학회 연구논문 초록집 Vol.2015 No.0

In recent years, there has been a rapid progress in the development of small-molecule organic photovoltaic cells with the power conversion efficiency reaching 12.0%. Besides high efficiency, the development of transparent conducting electrodes is of great importance for low cost and flexible organic solar cells. In this work, we have developed lowcost, efficient, semi-transparent small-molecule organic solar cells based on various alternative transparent electrodes, such as highly conductive polymers, ZnO, carbon nanotubes, doped C60, and conducting polymer/metal grid electrodes. These devices are carefully optimized by doping techniques for electrodes and interfacial layers. These results demonstrate that small-molecule organic solar cells based on alternative electrodes, optimized by doping technologies, have a promising future for practical applications in efficient, low-cost, flexible and semi-transparent device manufacturing.

Design and Synthesis of Small-Molecule Donor for High Efficient All-Small-Molecule Organic Solar Cells

김영훈,전성재,이형석,김지현,문두경 한국공업화학회 2020 한국공업화학회 연구논문 초록집 Vol.2020 No.-

Organic solar cells (OSCs) have considerable academic and industrial interest, owing to several advantages, such as their light weight, facile fabrication, low cost, good flexibility, and semitransparency. Introducing small-molecule donors (SMDs) to all-small-molecule OSCs has some merits relative to polymer donors, such as well-defined chemical structure, easy purification, definite molecular weight, and small batch-to-batch variations, which is important for commercial application. In this work, we designed and synthesized the SMDs with A-π-D-π-A architecture, based benzo[1,2-b:4,5-b’]dithiophene core which holds a larger coplanar core and extended conjugation length. The new SMDs was to match well with the small-molecule non-fullerene acceptors that usually have low-lying energy levels. These results show its promising for high performance OCSs, and suggest great process to design highly efficient SMDs in all-small-molecule OSCs

High-performance dopant-free conjugated small molecule-based hole-transport materials for perovskite solar cells

Azmi, Randi,Nam, So Youn,Sinaga, Septy,Akbar, Zico Alaia,Lee, Chang-Lyoul,Yoon, Sung Cheol,Jung, In Hwan,Jang, Sung-Yeon Elsevier 2018 Nano energy Vol.44 No.-

<P><B>Abstract</B></P> <P>Hole-transport materials are a crucial element influencing the efficiency, hysteresis, and stability of perovskite solar cells (PSCs). Current state-of-the-art hole-transport materials require additional oxidizing dopants to achieve sufficient hole-transport properties; however, these dopants are environmentally harmful while also deteriorating the stability of PSCs. The development of high-performance dopant-free hole-transport materials is an important goal in the field of PSCs. In this work, we developed novel conjugated small-molecule based dopant-free hole-transport materials for PSCs containing di(1-benzothieno)[3,2-b:2′,3′-d]pyrrole (DBTP) as a core unit. These small molecule hole-transport materials achieved higher hole mobility and interfacial charge transfer rates than optimally doped spiro-OMeTAD, the current-state-of-the-art hole-transport material. A low-temperature PSC device using a dopant-free small molecule hole-transport material displayed a PCE of 18.09% with negligible hysteresis, higher than a device using doped spiro-OMeTAD (17.82%). Notably, the hydrophobic nature of our dopant-free small molecule hole-transport materials afforded excellent air-storage stability of low-temperature PSCs (81% retention after 33 days), whereas the doped spiro-OMeTAD based PSCs rapidly degraded under identical conditions (< 1% retention after 33 days).</P> <P><B>Highlights</B></P> <P> <UL> <LI> Novel dopant-free hole-transport-materials for perovskite solar cells were developed. </LI> <LI> The face-on orientation enabled sufficiently high hole mobility without dopants. </LI> <LI> Low-temperature PSCs based on the dopant-free HTMs showed the efficiency of 18.09%. </LI> <LI> The dopant-free HTMs acted as passivation layers, providing excellent air stability. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>High-performance dopant-free small molecule hole-transport-materials (SM-HTMs) for perovskite solar cells (PSCs) are developed. The SM-HTMs possess appropriate energy levels with sufficient hole mobility to function as efficient HTM for PSCs without additional dopants. A low-temperature PSC (L-PSC) device using a dopant-free SM-HTM displayed a PCE of 18.09% with high air-storage stability, which is superior to a device using doped spiro-OMeTAD.</P> <P>[DISPLAY OMISSION]</P>

Solution-processed small molecular organic solar cells based on benzodithiophene with different terminal donor groups

( Sushil Bagde ),박한옥,이수형 한국공업화학회 2015 한국공업화학회 연구논문 초록집 Vol.2015 No.0

Intermolecular interactions have a critical role in determining the molecular packing and orientation of small molecule, leading to significant changes in their electrical and optical properties. Herein, we present two π-conjugated small molecules for use in solution-processed organic solar cells (OSCs) to elucidate the effect of terminal donor groups on the performance of benzodithiophene (BDT) based small molecules. Each small molecules have different terminal donor groups of hexylbithiophene (BDT(TTBT)2) or hexylphenyl-thiophene (BDT(PTBT)2). Various investigations into the molecules reveal that variation of the terminal groups not only influence the optical and electronic properties but also affect crystallization and morphology of the small molecules. BDT(TTBT)2 shows efficiency of 1.73% as a consequence of deep HOMO (Voc =0.81 V), improved charge delocalization and stronger light absorption (Jsc=4.75 mA/cm-2), when mild annealing was used as a result of improved texturing structures in morphology. BDT (PTBT)2 device rather shows moderate PCE of 1.22% with Jsc of 2.88 mA cm-2, Voc of 0.81V and FF of 0.52.

All-Small-Molecule Solar Cells Incorporating NDI-Based Acceptors: Synthesis and Full Characterization

Hong, Jisu,Ha, Yeon Hee,Cha, Hyojung,Kim, Ran,Kim, Yu Jin,Park, Chan Eon,Durrant, James R.,Kwon, Soon-Ki,An, Tae Kyu,Kim, Yun-Hi American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.51

<P>A series of naphthalene diimide (NDI)-based small molecules were synthesized as nonfullerene acceptors and incorporated in all-small-molecule solar cells. Three NDI-based small molecules, NDICN-T, NDICN-BT, and NDICN-TVT, were designed with different linkers between two NDI units to induce the different conjugation length and modulate the geometric structures of the NDI dimers. The small NDI-based dimer electron acceptors with slip-stacked structures that facilitate pi-pi stacking interactions and/or hinder excessive aggregation exhibited different morphological behaviors, such as miscibility or crystallinity in bulk heterojunction blends with 7,7'-(4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-bldithiophene-2,6-diyl)bis(6-fluoro-4-(5'-hexyl-[2,2'-bi-thiophen]-5-y1)benzo[c][1,2,5]thiadiazole) (DTS-F) electron donors. The photovoltaic devices prepared with NDICN-TVT gave the highest power conversion efficiency (PCE) of 3.01%, with an open-circuit voltage (V-oc) of 0.75 V, a short-circuit current density (J(sc)) of 7.10 mA cm(-2), and a fill factor of 56.2%, whereas the DTS-F:NDICN-T and DTS-F:NDICN-BT devices provided PCEs of 1.81 and 0.13%, respectively. Studies of the charge-generation properties, charge-transfer dynamics, and charge-transport properties for understanding the structure-property relations revealed that DTS-F:NDICN-TVT blend films with well developed domains and well-ordered crystalline structures performed well, whereas an excessive miscibility between DTS-F and NDICN-BT disrupted the crystallinity of the material and yielded a poor device performance.</P>

Synthesis, Characterization of Soluble Small Molecules Organic Solar Cells based on 2D-Benzodithiophene-Cyclopentadithiophene units

김두헌,한용운,문두경 한국공업화학회 2018 한국공업화학회 연구논문 초록집 Vol.2018 No.0

Organic photovoltaics (OPVs) are a promising technology for costeffective and scalable production of renewable energy. Current research in OPV materials focuses primarily on the design and synthesis of semiconducting polymers capable of both light absorption and charge transport. In order to develop OPV materials that exhibit not only favorable electronic properties but also batch-to-batch consistency, electroactive small molecules have recently received attention as alternatives to polymers. In this study, we report the design and synthesis of an acceptor- donor-donor-donor -acceptor (A-D'-D-D'-A) structured small-molecule materials based on a rigid 2-D benzodithiophene (BDT) central building block and cylcopentadithiophene (CPDT) linkers. The photo-physical, electrochemical and photovoltaic properties of the new two-small molecules organic solar cells have been studied and compared.

New donor-π-acceptor type molecules for small molecule organic solar cells

박주언,이윤구 한국공업화학회 2014 한국공업화학회 연구논문 초록집 Vol.2014 No.1

Recently, organic solar cells (OSCs) are attracting a lot of attention due to flexibility, low cost, light weight and large-area applications. Especially, OSCs using small molecules have attracted increasing attentions due to the advantages of small molecules over polymers which include simple synthesis and purification, well-defined structure, high charge carrier mobility and less batch-to-batch variation. In this study, we have synthesized asymmetric structured small molecules with di-(p-tolyl)amine as a donor unit and 2,1,3-benzothiadiazole as an acceptor unit for the organic photovoltaic devices. By changing the end groups attached on the acceptor unit of the molecule, we have investigated on the effect of the different electron withdrawing end groups on the small molecules. Thermal, optical and electrochemical properties of each molecule are measured and photovoltaic devices are successfully fabricated and characterized.

Change of Interface Property by Small Molecules with Hydroxyl Groups as the Electron Transfer Layer in Organic Solar Cell

진호철,김동근,( Ratna Dewi Maduwu ),( Sabrina Aufar Salma ),김주현 한국공업화학회 2018 한국공업화학회 연구논문 초록집 Vol.2018 No.0

As the fossil fuels that are currently being used are depleted, renewable energy industry recently has become active. And the one of renewable energy is solar cells. Especially, Organic solar cell (OSC) is a one of effective ways to convert solar source to electrical energy. Recently, many researchers have tried to achieve higher power conversion efficiency (PCE) of OSC by developing new semiconducting materials. In this study, we design the new small molecules with organic hydroxyl groups and intercalate between ZnO layer and active layer. Herein, hydroxyl groups induce the favorable interface dipole for these electron transfer layer (ETL) to enhance PCE. And we investigate the effect of interface dipole from hydroxyl groups on photovoltaic parameters.

Effect of Heterocyclic Anchoring Sequence on the Properties of Dithienogermole-Based Solar Cells

Walker, Bright,Han, Daehee,Moon, Mijin,Park, Song Yi,Kim, Ka-Hyun,Kim, Jin Young,Yang, Changduk American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.8

<P>The synthesis and characterization of two new small molecular donor materials, DTGe(ThFBTTh2)(2) and DTGe(FBTTh3)(2), are presented for application in organic solar cells. These two materials represent structural evolutions of the high-efficiency, dithienogermole (DTGe)-cored small molecule DTGe(FBTTh2)(2), in which the conjugation length in the backbone was extended by incorporating additional thiophene units. Using the same molecular framework, we have evaluated how the anchoring sequence of heterocyclic units influences material properties and function in solar cell devices. It was found that incorporating additional thiophene units into the backbone, regardless of the position in the molecular platform, caused a small reduction in band gaps; however, both highest occupied molecular orbitals and lowest unoccupied molecular orbital energy bands were at lower energies when the thiophenes were incorporated near the terminus of the molecule. The film morphologies of both materials could be controlled by either thermal or solvent vapor annealing to yield phase separation on the order of tens of nanometers and improved crystallinity. Peak power-conversion efficiencies of 3.6% and 3.1% were obtained using DTGe(ThFBTTh2)(2) and DTGe(FBTTh3)(2), after solvent vapor treatment and thermal annealing, respectively. Our study provides a detailed analysis of how the ordering sequence of heterocyclic building blocks influences the properties and function of organic solar cells.</P>