Highly Efficient Nonfullerene Polymer Solar Cells Enabled by a Copper(I) Coordination Strategy Employing a 1,3,4‐Oxadiazole‐Containing Wide‐Bandgap Copolymer Donor

Abstract

A novel wide-bandgap copolymer of PBDT-ODZ based on benzo[1,2-b:4,5-b' ]dithiophene (BDT) and 1,3,4-oxadiazole (ODZ) blocks is developed for efficient nonfullerene polymer solar cells (NF-PSCs). PBDT-ODZ exhibits a wide bandgap of 2.12 eV and a low-lying highest occupied molecular orbital (HOMO) level of -5.68 eV, which could match well with the low-bandgap acceptor of 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone)-5,5,11,11-tetrakis(4-hexylthienyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']-dithiophene (ITIC-Th), inducing a good complementary absorption from 300 to 800 nm and a minimal HOMO level offset (0.1 eV). The PBDT-ODZ:ITIC-Th devices exhibit a large open-circuit voltage (V ) of 1.08 eV and a low energy loss (E ) of 0.50 eV, delivering a high power conversion efficiency (PCE) of 10.12%. By adding a small amount of copper(I) iodide (CuI) as an additive to form coordination complexes in the active blends, much higher device performances are achieved due to the improved absorption and crystallinity. After incorporating 4% of CuI, the PCE is elevated to 12.34%, with a V of 1.06 V, a J of 17.1 mA cm and a fill factor of 68.1%. This work not only provides a novel oxadiazole-containing wide-bandgap polymeric donor candidate for high-performance NF-PSCs but also presents an efficient morphology-optimization approach to elevate the PCE of NF-PSCs for future practical applications.

Subtle Polymer Donor and Molecular Acceptor Design Enable Efficient Polymer Solar Cells with a Very Small Energy Loss

“…Besides, peak‐differentiating analysis showed that one more diffraction peak located at q xy = 0.386 Å −1 ( d = 16.3 Å, Figure S8, Supporting Information), which might originate from the backbone ordering due to the end‐group π–π stacking . Compared to the pristine polymer films, the (100) diffraction turned from semicircle to more preferred q xy direction, indicating the enhanced face‐on packing, which would be beneficial for vertical charge transport . The PNDT‐ST:Y6‐T binary blend showed higher ordered structures with multiple peaks than PNDT‐ST:Y6‐T binary blend.…”

“…The facile side chains provide the tunable bandgaps and molecular energy levels at the same time . For those reasons, BDT‐based donor polymers have dominated the most efficient PSCs . Compared with BDT, the extended π‐conjugation system of naphthodithiophene (NDT) is expected to produce the higher backbone coplanarity and affords stronger intermolecular orbital overlap, facilitating π‐electron delocalization along the backbone and inducing strong co‐facial π–π stacking for improving charge transport behavior .…”

Single‐Junction Polymer Solar Cells with 16.35% Efficiency Enabled by a Platinum(II) Complexation Strategy

“…We admit that such complexation strategy may be not unexceptionable from the perspective of industrialization. Only those polymer donors with specific polynitrogen heterocyclic skeletons can work well, and the complexation process increases the synthetic complexity and cost. Regardless of that, our work provides a new and efficient method for easy optimization of morphology in PSCs, which also can help us better understand the relationship of molecular structure and property.…”

“…In terms of active blend morphology, it is widely accepted that the nanoscale phase separation with the bicontinuous interpenetrating networks and the domain sizes in the range of 10–20 nm is critical for efficient exciton diffusion and dissociation . It is worth noting that such ideal morphology actually results from the joint effects of various factors, including the natural properties of the semiconductors (solubility, crystallinity, miscibility, etc.…”

Non‐Fullerene Small Molecule Acceptors Containing Barbituric Acid End Groups for Use in High‐performance OPVs

“…[1][2][3] Electron-deficient groups, such as rhodanine (RH), 4,5 1,3-indandione (IN), 6,7 and 1,1-dicyanomethylene-3-indanone (CNIN) 8,9 have been widely used as acceptor units, together with fused-ring-based electron-rich groups, such as carbazole (Cz), 10,11 fluorene (Flu), 12,13 indacenodithiophene (IDT), 14,15 and indacenodithienothiophene (IDTT). Non-fullerene acceptors (NFAs) composed of donor (D) and acceptor (A) units have been widely reported due to their high power conversion efficiencies (PCEs) exceeding 14%.…”