ABSTRACT
Although peripheral hetero-di-halogenation of non-fullerene acceptors (NFAs) would allow more precise optimization of molecular properties by providing the complementary advantages of two different halogens, thus enabling further improvements of organic solar cells (OSCs), hetero-di-halogenated NFAs are seldom prepared due to the challenging construction of building blocks with two adjacent hetero-halogens. Herein, three CH-series acceptors with hetero-di-halogenated central units, named CH-FC, CH-FB and CH-CB, are constructed successfully. PM6:D18:CH-FB-based OSCs afforded an attractive PCE of 19.0% due to tighter intermolecular packing at both the single-crystal and blended-film levels, more efficient charge transfer/dissociation, and superior film morphology compared to those of PM6:D18:CH-FC (PCE 18.41%) and PM6:D18:CH-CB (PCE 18.21%). Our work highlights the effectiveness of such a CH-series molecular platform in conducting hetero-di-halogenation and achieving high-performance OSCs, and will stimulate further exploration of hetero-substitution-based acceptors.
ABSTRACT
Halogenation of terminal of acceptors has been shown to give dramatic improvements in power conversion efficiencies (PCEs) of organic solar cells (OSCs). Similar significant results could be expected from the halogenation of the central units of state-of-the-art Y-series acceptors. Herein, a pair of acceptors, termed CH6 and CH4, featuring a conjugation-extended phenazine central unit with and without fluorination, have been synthesized. The fluorinated CH6 has enhanced molecular interactions and crystallinity, superior fibrillar network morphology and improved charge generation and transport in blend films, thus affording a higher PCE of 18.33 % for CH6-based binary OSCs compared to 16.49 % for the non-fluorinated CH4. The new central site offers further opportunities for structural optimization of Y-series molecules to afford better-performed OSCs and reveals the effectiveness of fluorination on central units.
ABSTRACT
High-quality transparent conductive materials are beneficial to improve the charge transfer and light transmittance and reduce the interface defects as well as the production cost of optoelectronic devices. A high threshold thickness of metal layer in oxide/metal/oxide (OMO) compound thin films leads to strong reflectance, especially in the near-infrared region, limiting the broad-spectrum device applications. Here, we propose a novel Zn doping strategy using the low-cost single-target sputtering technology to achieve the growth of Ag-Zn thin films (i.e., Zn-doped Ag) and introduce a trace amount of O2 to further obtain ultrathin Ag-Zn(O) films (thin-film thickness d ≤ 5 nm), which greatly improves the broad-spectrum characteristics of OMO films. Heterogeneous metal and gas doping technology effectively promotes the formation of two-dimensional continuous film growth. By combining the ultrathin Ag-Zn(O) layer with the MGZO (i.e., Mg- and Ga co-doped ZnO) oxide film grown by reactive plasma deposition, a typical broad-spectrum MGZO/Ag-Zn(O)/MGZO (50/5/50 nm)-OMO compound thin film exhibits an average transmittance of 91.6% in the wavelength range of 400-1200 nm and low sheet resistance. The broad-spectrum organic solar cells based on MGZO/Ag-Zn(O)/MGZO electrodes present a high power conversion efficiency of 15.35%, superior to those devices based on single-layer oxide electrodes. The distinguished performances are attributed to the ultrathin Ag-Zn(O) films in OMO, paving the way for applications in broad-spectrum optoelectronic and flexible electronic devices.
