Fluorene Side-Chained Benzodithiophene Polymers for Low Energy Loss Solar Cells

Here we design and synthesize one novel fluorene side-chained benzodithiophene (BDT) monomer for polymer solar cells (PSCs) donor. By copolymerizing this monomer with 4,7-di­(thiophen-2-yl)-2,1,3-benzo­thiadiazole (DTBT) or 4,7-di­(4-(2-ethylhexyl)-2-thienyl)-5,6-difluoro-2,1,3-benzo­thiadiazole (DT<i>ff</i>BT), two donor–acceptor (D–A) conjugated polymers PFBDT–DTBT and PFBDT–DT<i>ff</i>BT are prepared. PSCs are prepared with these polymers as donor and PC₇₁BM as acceptor. The maximum power conversion efficiency (PCE) of the two polymers PFBDT–DTBT and PFBDT–DT<i>ff</i>BT based PSCs is 7.13% (<i>V</i>_OC = 0.90 V, <i>J</i>_SC = 13.26 mA cm^–2, and FF = 0.598) and 7.33% (<i>V</i>_OC = 0.96 V, <i>J</i>_SC = 13.24 mA cm^–2, and FF = 0.577). The UV–vis absorption and electrochemical cyclic voltammetry test results show that F atoms in DT<i>ff</i>BT unit present an obvious influence on intermolecular effect and molecular energy levels of polymers. Furthermore, the energy loss of two PSCs devices in this work is confirmed to be 0.78 and 0.71 eV, lower than most results based on BDT PSCs devices, which is critical to obtain high PCE PSCs devices with a decent trade-off between <i>J</i>_SC and <i>V</i>_OC

High Extinction Coefficient Thieno[3,4‑<i>b</i>]thiophene-Based Copolymer for Efficient Fullerene-Free Solar Cells with Large Current Density

A thieno­[3,4-<i>b</i>]­thiophene-based donor polymer PTBTz-2 was employed to construct fullerene-free solar cell with the classical acceptor ITIC. Interestingly, due to the high extinction coefficients and wide absorption for these two materials, the active layer can harvest a larger fraction of the coverage solar spectrum even in ultrathin film. Furthermore, the simultaneous advantages of appropriate cascade energy level, well-balanced hole/electron mobility (μ_h/μ_e = 1.16), and low charge accumulation and recombination, make the PTBTz-2/ITIC-based solar cells exhibit an excellent power conversion efficiency of 10.92% with large short circuit current density of 20.34 mA cm^–2. The results indicate that fine-tailored thieno­[3,4-<i>b</i>]­thiophene-based polymers would be another type of promising donor materials, except for widely reported efficient benzo­[<i>d</i>]­[1,2,3]­triazole (BTA)- or benzo­[1,2-<i>c</i>:4,5-<i>c</i>′]-dithiophene-4,8-dione (BDD)-based polymers, and would enrich the reservoir of high-performance light-harvesting conjugated polymers