A Top‐Down Strategy to Engineer ActiveLayer Morphology for Highly Efficient and Stable All‐Polymer Solar Cells

Abstract

A major challenge hindering the further development of all‐polymer solar cells (all‐PSCs) employing polymerized small‐molecule acceptors is the relatively low fill factor (FF) due to the difficulty in controlling the active‐layer morphology. The issues typically arise from oversized phase separation resulting from the thermodynamically unfavorable mixing between two macromolecular species, and disordered molecular orientation/packing of highly anisotropic polymer chains. Herein, a facile top‐down controlling strategy to engineer the morphology of all‐polymer blends is developed by leveraging the layer‐by‐layer (LBL) deposition. Optimal intermixing of polymer components can be achieved in the two‐step process by tuning the bottom‐layer polymer swelling during top‐layer deposition. Consequently, both the molecular orientation/packing of the bottom layer and the molecular ordering of the top layer can be optimized with a suitable top‐layer processing solvent. A favorable morphology with gradient vertical composition distribution for efficient charge transport and extraction is therefore realized, affording a high all‐PSC efficiency of 17.0% with a FF of 76.1%. The derived devices also possess excellent long‐term thermal stability and can retain >90% of their initial efficiencies after being annealed at 65 °C for 1300 h. These results validate the distinct advantages of employing an LBL processing protocol to fabricate high‐performance all‐PSCs.

Optimal bulk morphologyviaside-chain engineering on non-fullerene acceptor for efficient organic solar cells

“…5 Furthermore, we simulated the exciton generation as a function of film depth for the three blend films by combining the depth-dependent spectra with an optical transfer matrix model. 43,45 above-discussed charge transport and recombination to explain the better J sc and FF of the PM6:Y-2Br-HD device, indicating that the underlying three-phase separated bulk morphology like the p-i-n structure is required.…”

Boosting the Fill Factor through Sequential Deposition and Homo Hydrocarbon Solvent toward Efficient and Stable All‐Polymer Solar Cells

“…[29][30][31] Basically, the solubility, miscibility, and crystallinity characteristics of the polymer acceptors and donors must be carefully taken into consideration in order to produce high-quality, thoroughly blended, and morphologically stable pseudo-bilayer blend films for all-PSCs. [26,[32][33][34][35] Therefore, it is essential to take comprehensive consideration of the SD method and solvent selection that can effectively promote the photovoltaic performance and stabilities of the all-PSCs.…”

Visualization of sub-nanometer scale multi-orientational ordering in thin films of polymer/non-fullerene acceptor blends

“…The thermodynamic conditions and kinetics of solvent evaporation during processing affect the morphology of BHJ blends at multiple length scales. 20,[24][25][26][27][28][29][30][31][32] Large-scale phaseseparated morphologies have been observed for many polymer/polymer and polymer/fullerene systems. [33][34][35][36] Due to the crystallisation of both donor polymer and NFA, phase separations into amorphous polymer/crystalline NFA and semicrystalline polymer/crystalline NFA can take place.…”