Nanographene–Osmapentalyne Complexes as a Cathode Interlayer in Organic Solar Cells Enhance Efficiency over 18%

Abstract

Development of power conversion efficiency (PCE) and short-term stability are still huge challenges that restrict the actual industrialization of OSCs. [5,6] There has been much exploration of the state-of-art photovoltaic performance, with methods that mainly concentrate on the molecular design, structure modification of devices, and the construction of active layers. [7][8][9] Through innovative molecular design and matching with suitable donors, the Y6 system has opened a new vista in which the efficiency of nonfullerene solar cells (NFSC) approached 16%. [10] To date, subsequent optimizations have brought a brighter future with the PCE in single-junction devices exceeding 18%. [11][12][13][14] Together with molecular innovation, interface engineering also improves the device performances continually. Gene rally, interface engineering implies that through insertion of a single or double interlayer between an active layer and a cathode or anode to improve the indirect contact between them, and further regulation of the morphology or work function of electrodes, the devices can be improved. Included amongst the most popular interfacial materials, there are several main types: [15] metal oxides (MO), including the commonly used ZnO [16] and MoOx, alcohol-soluble polymers and small molecules such as amino PDINO [17] and PFN-Br, [18] Interface engineering is a critical method by which to efficiently enhance the photovoltaic performance of nonfullerene solar cells (NFSC). Herein, a series of metal-nanographene-containing large transition metal involving d π -p π conjugated systems by way of the addition reactions of osmapentalynes and p-diethynyl-hexabenzocoronenes is reported. Conjugated extensions are engineered to optimize the π-conjugation of these metal-nanographene molecules, which serve as alcohol-soluble cathode interlayer (CIL) materials. Upon extension of the π-conjugation, the power conversion efficiency (PCE) of PM6:BTP-eC9-based NFSCs increases from 16% to over 18%, giving the highest recorded PCE. It is deduced by X-ray crystallographic analysis, interfacial contact methods, morphology characterization, and carrier dynamics that modification of hexabenzocoronenes-styryl can effectively improve the short-circuit current density (J sc ) and fill factor of organic solar cells (OSCs), mainly due to the strong and ordered charge transfer, more matching energy level alignments, better interfacial contacts between the active layer and the electrodes, and regulated morphology. Consequently, the carrier transport is largely facilitated, and the carrier recombination is simultaneously impeded. These new CIL materials are broadly able to enhance the photovoltaic properties of OSCs in other systems, which provides a promising potential to serve as CILs for higher-quality OSCs.

Effect of Arylmethylene Substitutions on Molecular Structure, Optoelectronic Properties and Photovoltaic Performance of Dithienocyclopentafluorene‐Based Small‐Molecule Acceptors

“…For DTCFDV-IC, one can find that the S atom from thiophene ends in the central D unit can form weak S•••O noncovalent interaction with O atoms from the IC group, which can induce planar backbone structure to enhance π-π stacking and molecular packing in solid state, thus leading to better charge transport ability. [10] From another aspect, the conjugated aryl chains far away from the backbone of the ladder-type central unit (DTCFV) owing to the inserted methylene in DTCF moiety can improve the rigidity of these SMAs and promote to form closer intermolecular π-π stacking (see the side view in Figure S11 in the Supporting Information), which will be beneficial for obtaining high charge carrier mobility. As displayed in Figure 4, we can find that the electron distributions of HOMO levels are mainly delocalized from the ladder-type central unit (DTCF or DTCFV) to the A unit (IC) to a certain extent, whereas the electron densities of LUMO…”

“…[22] Thereafter, PCEs of PSCs based on this kind of SMAs, so-called Y-series SMAs, boomed rapidly and exceeded 18 %. [1][2][3][4][5][6][7][8][9][10] Including ITIC and Y6, most of high-performance SMAs possess an acceptor-donor-acceptor (AÀ D-A) type structural skeleton, where a ladder-type fused ring (like IDTT, TPBT) was used as the central donor (D) unit and an electron-withdrawing unit is employed as the end-capping acceptor (A) group. [21][22][23][24][25] Here, it should be noted that the ladder-type central unit is fused by an electron-deficient core (e. g. benzothiadiazole) with an electron-rich unit (typically dithienothiophen[3.2-b]pyrrole) in Y-series SMAs.…”

“…In recent years, bulk heterojunction (BHJ) polymer solar cells (PSCs) are steadily and rapidly developing with power conversion efficiencies (PCEs) over 18 % [1][2][3][4][5][6][7][8][9][10] due to the continuous optimization of the molecular structure of materials, [11][12][13] the configuration and fabrication process of photovoltaic devices. [14][15][16] This outstanding achievement is mainly ascribed to the fact that fullerene-based acceptors were substituted by the springing up of new nonfullerene small-molecule acceptors (SMAs) thanking to their superior optical absorption properties, easily tunable molecular energy levels, and potential for relatively low-cost production processes.…”

18.77 % Efficiency Organic Solar Cells Promoted by Aqueous Solution Processed Cobalt(II) Acetate Hole Transporting Layer

“…[3] In addition to the advances in photoactive materials, interfacial layers also play an equally important role in improving not only the device performance but also the device stability of OSCs. [4] Thei nterfacial layers (hole transporting layer and electron transporting layer) inserted between the photoactive layer and the electrodes aim to tune the work function, forming an Ohmic contact, minimizing the energy barrier and improving the charge selectivity of electrodes. [5] Note that numerous electron transporting layers (ETLs) have been developed for high performance OSCs,but the development on hole transporting layers (HTLs) still lack far behind.…”

Binary and Ternary Polymer Solar Cells Based on a Wide Bandgap D‐A Copolymer Donor and Two Nonfullerene Acceptors with Complementary Absorption Spectral

“…In recent years, with the emergence of nonfullerene small molecule acceptors (NFSMA), [1][2][3][4][5][6][7] and non-fullerene polymers, [8,9] polymer solar cells (PSCs) based on bulk heterojunction (BHJ) have attained rapid development in power conversion efficiency (PCE) in the range of 17-18 % [10][11][12][13][14][15][16] for single junction based active layers. It is predicted that after the selection of appropriate polymer donor and NFSMAs, the PCE can be increased upto 20 % with high stability [17,18] and may be the potential candidate for future eco-friendly commercial application in indoor as well greenhouses.…”