A Maverick Asymmetrical Backbone with Distinct Flanked Twist Angles Modulating the Molecular Aggregation and Crystallinity for High Performance Nonfullerene Solar Cells

Abstract

energy source. [1][2][3][4] The past few years have witnessed the rapid progress of nonfullerene n-type acceptors and the PCE of nonfullerene-based PSCs devices have already surpassed 13% for single-junction devices. [5][6][7][8][9] To achieve efficient nonfullerene PSCs and mature fully from research into cost effective products, it is of critical importance not only to design high-performance small molecular acceptors (SMAs), but also to develop matching donor polymers, as well as to deeply understand the mechanism of the coordinated microstructure interactions between donor and acceptor components. [10][11][12][13][14][15] Key and fundamental strategies for designing high-effciency nonfullerene PSC devices are absorption spectrum and energy level. The donor and acceptor components should possess complementary absorptions and high extinction coefficient to enhance light harvesting to achieve high J SC . [16,17] The matching energy levels are crucial for donor and acceptor to ensure efficient driving force of exciton dissociation, to minimize voltage loss and thus to guarantee high V OC . However, the troublesome tradeoff between high V OC and J SC is inevitable which is the big challenge for further improving the PSCs performance. [18,19] In addition, the most difficult and complicated problem is how to precisely modulate the microstructure of the blending system. The donor should exhibit good morphology compatibility with the acceptor, including suitable crystallinity, appropriate aggregation, face-on orientation, and moderate domain size, and thus to achieve excellent charge transport and high fill factor (FF). [20][21][22] Therefore, establishing universal and general guideline of rational designing compatible D/A structure is extremely urgent and important for nonfullerene PSCs.Benzo[1,2-b:4,5-b′]dithiophene (BDT) and dithieno[2,3d:2′,3′-d′]benzo[1,2-b:4,5-b′]dithiophene (DTBDT) are the dominant backbones for donor polymers because of their planar framework, showing the most high performance in PSCs. [23][24][25][26][27][28][29][30] Most researchers focus on the side chain engineering of BDT-and DTBDT-based polymers and demonstrate that optimized side-chain can easily control polymer packing In this work, a new asymmetrical backbone thienobenzodithiophene (TBD) containing four aromatic rings is designed, and then four polymers PTBD-BZ, PTBD-BDD, PTBD-FBT, and PTBD-Tz are synthesized. The planar and high degree of π-conjugation configuration can guarantee effective charge carrier transport and the distinct flanked dihedral angles between the TBD core and conjugated side chain can subtly regulate the molecular aggregation and crystallinity. The four polymer/3,9-bis(2-methylene-(3-(1,1dicyanomethylene)-indanone)-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]-dithiophene (ITIC) blending films exhibit predominantly face-on orientation. The photovoltaic devices based on wide bandgap polymers PTBD-BZ and PTBD-BDD achieve power conversion efficiencies (PCEs) as high as 12.02% and...

Elevated Photovoltaic Performance in Medium Bandgap Copolymers Composed of Indacenodi-thieno[3,2-b]thiophene and Benzothiadiazole Subunits by Modulating the π-Bridge

“…However, the dropped PCE was observed after further fluorination in PIDTT-TFBT, which was mainly restricted by undesired morphology for photoactive layer as a result of strong aggregation even if in the condition of the upshifted V OC . Our preliminary results can demonstrate that modulating the π-bridge in polymer backbone was an effective method with the aim to enhance the performance for solar cell.Polymers 2020, 12, 368 2 of 22 (CPs) and n-type small molecules (i.e., PCBM or ITIC etc.,) have received an increasing attention because of excellent superiorities, such as, low-cost, light weight, mechanical flexibility, and low temperature solution processing [3][4][5][6][7]. To date, power conversion efficiencies (PCEs) of PSCs have surpassed over 11% [8] in fullerene-accepter system and 15% in non-fullerene system [9], respectively, profited by the design of novel materials, optimization of morphology for photoactive layer and the deepened understanding of the structure-performance relationship [4,[10][11][12][13][14][15][16][17][18].…”

Solution-processible Cd-doped ZnO nanoparticles as an electron transport layer to achieve high performance polymer solar cells through improve conductivity and light transmittance

“…6. shows the Nyquist plot of the devices with and without Cd-doped buffer layer, which was measured in dark condition, 5% CZO ETL significantly lower than other devices, indicating more efficient electron extraction and reducing interfacial charge recombination at interface [38][39][40][41][42].…”

Fluorination Effect for Highly Conjugated Alternating Copolymers Involving Thienylenevinylene-Thiophene-Flanked Benzodithiophene and Benzothiadiazole Subunits in Photovoltaic Application

“…The photovoltaic performance of BHJ PSCs was highly dependent on the semiconductor materials used as the photoactive layer. Thus, tremendous efforts in the past decades have been devoted to exploring excellent semiconducting materials, such as conjugated copolymers (CPs) and small molecules (SMs), and the use of various additives to modulate the morphology and optimization of processing techniques [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34]. Recently, with the help of novel materials, improved morphology, much more profound understanding of the structure-performance correlation and the photon-to-electron conversion mechanism, and power conversion efficiencies (PCEs) for PSCs in the single-junction module of over 11% in fullerene systems [35] and over 16% in non-fullerene systems [36][37][38][39] were achieved.…”

“…It has proved that constructing donor-acceptor (D-A) type CPs and/or SMs appears to be one of the most simplistic, promising, attractive, and successful strategies, since the alternating D-A conjugated blocks in the polymer backbone not only led to the reduction of the band gap by hybridizing the highest occupied molecular orbital (HOMO) with the lowest unoccupied molecular orbital (LUMO), but also enhanced the inter-and intra-molecular interactions directly governing the molecular ordering and π-π stacking for conjugated materials in the solid state. As a consequence, the molecular properties for D-A type semiconducting materials, such as frontier energy levels, absorption, dipole moment, planarity of the backbone, intermolecular interaction, charge transport characteristics, and morphology could be fine-modulated by judiciously selecting D and A units and properly combining them, assisted by adjusting the photo-induced intra-molecular charge transfer (ICT) effect [7,[20][21][22][23][24]26,[36][37][38][39][40][41]. In order to maximize the PCE of PSCs, it was of critical importance that, on one hand, enlarging the difference as much as possible between the E HOMO of donor and E LUMO of acceptor could obtain a larger open-circuit voltage (V OC ), meanwhile the suitable E LUMO paired with the electron acceptor was also juggled for charge separation and transport, while on the other hand, reducing the optical band gap toward harvesting more photons by up-shifting the E HOMO or down-shifting the E LUMO was anticipated to yield higher short-circuit current density (J SC ) [7,8].…”