Boosting Up Performance of Inverted Photovoltaic Cells from Bis(alkylthien-2-yl)dithieno[2,3‑<i>d</i>:2′,3′‑<i>d</i>′]benzo[1,2‑<i>b</i>:4′,5′‑<i>b</i>′]di thiophene-Based Copolymers by Advantageous Vertical Phase Separation

The photovoltaic cells (PVCs) from conjugated copolymers of PDTBDT-BT and PDTBDT-FBT with 5,10-bis­(4,5-didecylthien-2-yl)­dithieno­[2,3-<i>d</i>:2′,3′-<i>d</i>′]­benzo­[1,2-<i>b</i>:4,5-<i>b</i>′]­dithiophene as electron donor moieties and benzo­thiadiazole and/or 5,6-difluorobenzo­thiadiazole as electron acceptor moieties are optimized by employing alcohol-soluble PFN (poly­(9,9-bis­(3′-(<i>N</i>,<i>N</i>-dimethyl­amino)­propyl)-2,7-fluorene)-<i>alt</i>-2,7-(9,9-dioctyl­fluorene)) as cathode modification interlayer. The power conversion efficiencies (PCEs) of inverted PVCs (<i>i-</i>PVCs) from PDTBDT-BT and PDTBDT-FBT with devices configuration as ITO/PFN/active layer/MoO₃/Ag are increased from 4.97% to 8.54% and 5.92% to 8.74%, in contrast to those for the regular PVCs (<i>r-</i>PVCs) with devices configuration as ITO/PEDOT:PSS/active layer/Ca/Al under 100 mW/cm² AM 1.5 illumination. The optical modeling calculations and X-ray photoelectron spectroscopy (XPS) investigations reveal that the <i>r-</i>PVCs and <i>i-</i>PVCs from the copolymers exhibit similar light harvesting characteristics, and the enhancements of the PCEs of the <i>i-</i>PVCs from the copolymers are mainly contributed to the favorable vertical phase separation as the strongly polymer-enriched top surface layers and slightly PC₇₁BM (phenyl-C₇₁-butyric acid methyl ester)-enriched bottom surface layers are correspondingly connected to the anodes and cathodes of the <i>i-</i>PVCs, while they are opposite in the <i>r-</i>PVCs. As we known, it is the first time to experimentally verify that the <i>i-</i>PVCs with alcohol-soluble conjugated polymers cathode modification layers enjoy favorable vertical phase separation

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