Sub-glass transition annealing enhances polymer solar cell performance

Abstract

Thermal annealing of non-crystalline polymer:fullerene blends typically results in a drastic decrease in solar cell performance. In particular aggressive annealing above the glass transition temperature results in a detrimental coarsening of the blend nanostructure. We demonstrate that mild annealing below the glass transition temperature is a viable avenue to control the nanostructure of a non-crystalline thiophenequinoxaline copolymer:fullerene blend. Direct imaging methods indicate that coarsening of the blend nanostructure can be avoided. However, a combination of absorption and luminescence spectroscopy reveals that local changes in the polymer conformation as well as limited fullerene aggregation are permitted to occur. As a result, we are able to optimise the solar cell performance evenly across different positions of the coated area, which is a necessary criterion for large-scale, high throughput production.

Barrierless Free Charge Generation in the High‐Performance PM6:Y6 Bulk Heterojunction Non‐Fullerene Solar Cell

“…A second example where a very low temperature dependence of CT dissociation was being proposed is the blend of TQ1 with PCBM . This blend exhibits a reasonably large Δ E S1,CT (>0.2 eV), but more importantly a large energetic disorder of the ionization energy (IE) and the electron affinity (EA) …”

Organic Solar Cell Materials toward Commercialization

“…b) AFM images (left) and TEM images (right) of TQ1:PC 61 BM blend films after annealing for 10 min at the indicated temperatures. Reproduced with permission . Copyright 2014, The Royal Society of Chemistry.…”

Fullerene mixtures enhance the thermal stability of a non-crystalline polymer solar cell blend

“…[5][6][7][8] However, polymer:fullerene blends tend to coarsen when heated above T blend g , which for the majority of currently investigated materials lies below the required processing and operating temperatures. In addition, micrometer-sized fullerene crystallites grow, 9,10 which are detrimental for the device performance.…”

“…In addition, micrometer-sized fullerene crystallites grow, 9,10 which are detrimental for the device performance. 5,8,11 One increasingly explored route to improve the thermal stability of polymer:fullerene blends is the use of fullerene mixtures, which either hinders crystallization of the fullerene acceptor, [12][13][14] or results in the controlled nucleation of submicrometer-sized fullerene crystals. 15,16 Here, mixtures of phenyl-C 61 -butyric acid methyl ester (PC 61 BM, Fig.…”

“…8 Devices with an architecture of glass/ITO/PEDOT:PSS/active layer/LiF/Al were prepared by spin-coating active layers from 25 g L À1 oDCB solution on top of PEDOT:PSS (Clevios P VP Al 4083, Heraeus; annealed at 125 C for $15 min). After spin-coating of the active layer (thickness $ 90 nm), annealing for 10 min at 100, 140 or at even higher temperatures (160-180 C) was performed (in dark and in a nitrogen filled glove box), followed by evaporation of the metal electrodes.…”