Strategic Halogen Substitution to Enable High‐Performance Small‐Molecule‐Based Tandem Solar Cell with over 15% Efficiency

Abstract

Small molecules have been recently highlighted as active materials owing to their facile synthesisis method, well‐defined molecular structure, and highly reproducible performance. In particular, optimizing bulk heterojunction (BHJ) morphologies is important to achieving high performance in solution‐processable small molecule solar cells (SM‐SCs). Herein, a series of benzodithiophene‐based active materials with different halogen atoms substituted at the end‐group, are reported, as well as how these halogen atoms affect the morphology of BHJ architectures through microstructure analyses. Materials with chlorine atoms show a well‐mixed morphology and interpenetrating networks when blended with [6,6]‐phenyl‐C71‐butyric acid methyl ester, facilitating effective charge transportation. This controlled morphology helps attain excellent performance with a power conversion efficiency (PCE) of 10.5% and a highest fill factor of 78.0% without additives. In addition, it can be applied to two‐terminal (2T)‐tandem solar cells, attaining an outstanding PCE of up to 15.1% with complementary absorption in the field of the 2T‐tandem solar cells introducing the SM‐SCs. These results suggest that tailoring interactions with halogen atoms is an effective way to control BHJ architectures, thereby achieving remarkable performance in SM‐SCs.

Ionically Gated Small-Molecule OPV: Interfacial Doping of Charge Collector and Transport Layer

“…Organic photovoltaics (OPVs) is one of the competitive technologies in the modern renewable energy sector, which is capable of partially meeting the needs of power generation due to many advantages such as low cost, extreme flexibility, lightweight, and large-area manufacturing . Since the pioneering work by Tang on two-layer OPV cells based on the molecular donor–acceptor structure of CuPc and the perylene tetracarboxylic derivative with a power conversion efficiency (PCE) of about 1%, significant progress has been achieved in understanding and improvement of OPV systems, leading to a PCE of over 14% in single-junction and over 15% in tandem small-molecule OPV-based devices. Moreover, in the recent couple of years, even greater achievements in OPV have been reported, related to the discovery and usage of new materials and better architectures, and high power conversion efficiencies have been recorded, with PCEs of 17–18%, , that are not so far from the commercialization threshold.…”

A-D-A Type Semiconducting Small Molecules with Bis(alkylsulfanyl)methylene Substituents and Control of Charge Polarity for Organic Field-Effect Transistors

“…The red-shifted absorption for IDSIC-4Cl compared to that of IDSIC-4F can be attributed to two reasons: First, the empty 3d orbitals in Cl atoms can accept π-electrons, enhancing the electron-withdrawing ability of the terminal INCN group. Second, as the density functional theory (DFT) calculation result shows, the larger dipole moment of C–Cl (than C–F) can enhance the ICT interaction in IDSIC-4Cl. − In the thin film, the broader and significantly red-shifted spectra (by 50–70 nm) than those in solution are due to the enhanced intermolecular packing interactions in the solid state . The absorption maxima (λ max/film ) were determined to be 737, 737, 760, and 792 nm for IDSIC, IDSIC-4F, IDSIC-4Cl, and IDSTIC, respectively.…”

“…The larger dipole moment leads to a more pronounced ICT character with the deeper LUMO in IDSIC-4Cl compared with IDSIC-4F. 44,51 Electrical Properties. To study the charge transport properties of the IDT-based small molecular semiconductors, top-gate and bottom-contact (TGBC) OFETs were fabricated as shown in Figure 3a.…”

Recent Advances Toward Highly Efficient Tandem Organic Solar Cells

“…Lee and coworkers developed BDTID‐Cl, which realized a high V oc of 0.95 V, a J sc of 14.1 mA cm −2 , an FF of 78%, and a PCE of 10.5% in single‐junction devices. [ 127 ] Using PTB7‐Th:O6T‐4F:PC 71 BM ternary blend in the top subcell, the tandem devices could harvest a wide range of sun light from 300 to 1000 nm, boosting the PCE up to 15.1%. The chemical structures of the small molecule donors are shown in Scheme .…”

“…[ 33 ] To circumvent that, the pH neutral PEDOT:PSS analogues of m ‐PEDOT:PSS and highly conductive poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PH100) with high viscosity were used. [ 21,33,38–40,58,70,75–77,85,97,99,102,122,127–129,132,138,144,164,208 ] Zhou and coworkers found that PEDOT:PSS with surfactant deposited on top of nonfullerene‐based tandem OSCs might lead to chemical reaction between PEDOT:PSS and the NFA (IT‐4F), which would be detrimental to the device performance. [ 100 ] To avoid the direct deposition of PEDOT:PSS on top of the active layer, they introduced a hydrogen molybdenum bronze (H x MoO 3 ) layer between the bottom active layer and PEDOT:PSS.…”