Enhanced Photodynamic of Carriers and Suppressed Charge Recombination Enable Approaching 18% Efficiency in Nonfullerene Organic Solar Cells

Regulation of the exciton generation, diffusion, and carrier transport, as well as optimization of the non-radiative energy loss could further overcome the power conversion efficiency limitation of organic solar cells. However, the relationship between exciton properties and non-radiative energy loss has seldom been investigated. Herein, taking D18-series devices as the research model, the exciton diffusion length (LD) and hole transfer dynamics can be remarkably improved by the variation of electron-withdrawing halogen and the non-radiative energy loss simultaneously can be suppressed. By combining the analysis results of hole transfer, exciton diffusion, charge separation, and recombination, this work demonstrates that the photo-induced exciton in the chlorinated polymer donor can diffuse to a longer distance within the effective exciton lifetime, suppress the exciton recombination, and enhance device performance. The results define the relationship between the exciton behaviors and non-radiative energy loss and further reveal the significance of controlling the bulk heterojunction with superior photo-physical properties

Large branched alkylthienyl bridged naphtho[1,2-<i>c</i>:5,6-<i>c</i>′]bis[1,2,5]thiadiazole-containing low bandgap copolymers: Synthesis and photovoltaic application

<p>Two donor-acceptor (D-A) type low bandgap (LBG) alternating conjugated copolymers containing larger conjugation planarity and stronger electro-withdrawing ability naphtho[1,2-<i>c</i>:5,6-<i>c</i>′]bis[1,2,5]thiadiazole (NT) unit, namely, poly[4,8-bis(5-(<i>n</i>-octylthio)thien-2-yl)-benzo[1,2-<i>b</i>:4,5-<i>b</i>′]dithiophene-2,6-diyl-<i>alt-</i>4,9-bis(4-(2-decyltetradecyl)thien-2-yl)naphtho- [1,2-<i>c</i>:5,6-<i>c</i>′]bis[1,2,5]thiadiazole-5,5′-diyl] (<b>PBDT-TS-DTNT-DT</b>) and poly[4,8-bis(triiso-propylsilylethynyl)benzo[1,2-<i>b</i>:4,5-<i>b</i>′]dithiophene-2,6-diyl-<i>alt</i>-4,9-bis(4-(2-decyltetradecyl)-thien-2-yl)naphtho[1,2-<i>c</i>:5,6-<i>c</i>′]bis[1,2,5]thiadiazole-5,5′-diyl] (<b>PBDT-TIPS-DTNT-DT</b>), were prepared by the palladium-catalyzed Stille polycondensation and characterized by gel permeation chromatography (GPC), UV-Vis absorption, thermal gravimetric analysis (TGA), cyclic voltammetry (CV) <i>etc</i>. <b>PBDT-TS-DTNT-DT</b> and <b>PBDT-TIPS-DTNT-DT</b> show the broader absorption and deeper highest occupied molecular orbital (HOMO) energy level approximately −5.45 and −5.62 eV, respectively. Bulk-heterojuction solar cells based on the resulted polymers and [6,6] phenyl-C₆₁ butyric acid methyl ester (PC₆₁BM) blends, with the device configuration of ITO/PFN/polymer:PC₆₁BM/MoO₃/Ag were prepared and investigated. The results showed the power conversion efficiency (PCE) of 2.67% for <b>PBDT-TS-DTNT-DT</b>/PC₆₁BM (w:w, 1:2) and 0.64% for <b>PBDT-TIPS-DTNT-DT</b>/PC₆₁BM (w:w, 1:1), with relatively high open-circuit voltage (<i>V</i>_OC) of 0.86 and 1.05 V, small short-circuit current (<i>J</i>_SC) of 5.41 and 0.97 mA cm⁻² and moderate fill factor (<i>FF</i>) of 57.8% and 62.4%, under an AM1.5 simulator (100 mWcm⁻²), respectively.</p

Synergy Effect of Symmetry-Breaking and End-Group Engineering Enables 16.06% Efficiency for All-Small-Molecule Organic Solar Cells

Molecular innovation is an urgent necessity to realize efficient all-small-molecule organic solar cells (ASM-OSCs). Asymmetric strategy and end-group engineering have been widely utilized for efficient photovoltaic materials with great success. However, the synergistic effect of the asymmetric strategy combined with end-group engineering on blend film morphology and photovoltaic performance remains insufficiently explored. In this vein, two asymmetric small molecule donors with thiophene/thiazolyl side chains and different end-groups of 3-(2-ethylhexyl)-2-thioxo-4-thiazolidinone (Reh) and cyanoacetic acid esters (CA), W2-CA and W2-Reh, were designed to gain insight into the combined effects of symmetry-breaking and end-group engineering. Compared to W2-Reh, W2-CA exhibits a preferable face-on orientation and good bicontinuous phase-separated morphology, which benefit improving carrier mobility and ensuring a high-efficiency charge transfer pathway in the blended films. 16.06% power conversion efficiency (PCE) is achieved in W2-CA-based ASM-OSCs, one of the highest efficiencies reported up to now for binary ASM-OSCs. A promising avenue for high-efficiency small molecule donor design is provided to achieve efficiency ASM-OSCs