Ternary Blended Fullerene‐Free Polymer Solar Cells with 16.5% Efficiency Enabled with a Higher‐LUMO‐Level Acceptor to Improve Film Morphology

Abstract

achieved power conversion efficiencies (PCEs) greater than 15% in singlejunction binary devices. [13,14] However, the performance of the binary system is still largely limited by the material's own properties (narrow absorption, small crystallinity, low charge mobility, strong recombination, etc.). In order to overcome these limitations, the strategy of adding a third component to the binary system, e.g., ternary solar cell approach, has come into being and shown wideranging applicability in improving the solar cell device function. The addition of a structurally similar third component can either extend the absorption range of solar emission spectrum, tune the frontier molecular orbital (FMOs) levels such as through forming homogeneous donor or acceptor phases, [15,16] modulate the active layer's electric property by improving the film morphology, [17][18][19] or tune the acceptor phase optical property, [20] which can promote either the device short-circuit current density (J sc ), or open-circuit voltage (V oc ), or fill factor (FF), and finally, boost power conversion efficiencies with the values reaching over 13% recently. [21][22][23][24][25][26] The ternary approach, by introducing a smaller bandgap nonfullerene acceptor as a near infrared (NIR) absorber to increase the device J sc of fullerene-free binary blended material systems, hereafter named as the "current-increased" Ternary approaches to solar cell design utilizing a small bandgap nonfullerene acceptor as the near infrared absorber to increase the short-circuit current density always decreases the open-circuit voltage. Herein, a highly efficient polymer solar cell with an impressive efficiency of 16.28 ± 0.20% enabled by an effective voltage-increased ternary blended fullerene-free material approach is reported. In this approach, the structural similarity between the host and the higher-LUMO-level guest enables the two acceptors to be synergized, obtaining increased open-circuit voltage and fill factor and a small increase of short-circuit current density. The same beneficial effects are demonstrated by using two host binary systems. The homogeneous fine film morphologies and the π-π stacking patterns of the host blend are well maintained, while larger donor and acceptor phases and increased lamellar crystallinity, increased charge mobilities, and reduced monomolecular recombination can be achieved upon addition of the guest nonfullerene acceptor. The increased charge mobilities and reduced monomolecular recombination not only contribute to the improved fill factor but also enable the best devices to be fabricated with a relatively thicker ternary blended active layer (110 vs 100 nm). This, combined with the absorption from the added guest acceptor, contribute to the increased short-circuit current.

As‐Cast Ternary Organic Solar Cells Based on an Asymmetric Side‐Chains Featured Acceptor with Reduced Voltage Loss and 14.0% Efficiency

“…Scattering of PM6 : TOBDT was less distinct, and after the addition of IDIC , a slightly larger phase separation scale of 69.8 nm was observed, which might be due to the induced crystallization of PM6 . Similar results were found in the previous report that after the addition of IDIC , PM6 formed much larger fibers . The center‐to‐center distance of 69.8 nm is still a suitable length scale for efficient exciton dissociation, and in the meanwhile, charge‐transporting property is promoted, enabling ternary devices to show better performance.…”

“…In addition to the innovation of active materials development, device optimization processes including solvent additives, interfacial engineering, and ternary strategies, also play critical roles in improving the performance of solar cells. Among these, constructing ternary solar cells, which have two donor materials paired with one acceptor (2D/1A) or one donor paired with two acceptors (1D/2A), is a simple and effective way to improve the overall device performance . The successful ternary system usually shows complementary absorption, reduced voltage loss, minimal charge recombination, and balanced charge transport process .…”

Beyond Ternary OPV: High‐Throughput Experimentation and Self‐Driving Laboratories Optimize Multicomponent Systems

“…With the development of novel nonfullerene acceptors fundamental performance limitations of fullerene‐based organic solar cells (OSCs) have been overcome 1,2. In the currently highest performing system PM6:Y6 ternary additives are used to improve charge carrier lifetime and mobility resulting in significantly improved performance with efficiencies up to 16.5% 3,4. Typically in ternary systems the host donor:acceptor (D:A) ratio is kept constant, while only the content of additive is varied due to limited experimental resources.…”

Flexible All‐Solution‐Processed Organic Solar Cells with High‐Performance Nonfullerene Active Layers

“…2) A deep‐lying highest occupied molecular orbital (HOMO) level. Both Y6 and IT‐4F with F substitution have deep HOMO levels of −5.62 and −5.71 eV, respectively 38. The corresponding polymer donor used to match with Y6 and IT‐4F is also F substituted (PBDB‐T‐2F) with a deep HOMO of −5.54 eV 38.…”

“…Both Y6 and IT‐4F with F substitution have deep HOMO levels of −5.62 and −5.71 eV, respectively 38. The corresponding polymer donor used to match with Y6 and IT‐4F is also F substituted (PBDB‐T‐2F) with a deep HOMO of −5.54 eV 38. The deep HOMO level of the PBDB‐T‐2F is much lower‐lying than the Fermi level of the PEDOT:PSS that would cause a charge extraction issue and an open‐circuit voltage ( V OC ) drop.…”