Volatile Solvent Additives Enabling High-Efficiency Organic Solar Cells without Thermal Annealing

Abstract

Additive strategy is considered to be an effective way to achieve high-efficiency organic solar cells (OSCs). However, for heat-sensitive material systems, such as D18 and its derivatives, solvent additives with high-boiling points that need to be fully removed by high-temperature annealing often fail to optimize the device performance. Herein, based on the D18-Cl:Y6-based device, we chose the volatile solvent tetrahydrofuran (THF) as the solvent additive, which can achieve effects similar to high-boiling-point additives without thermal annealing. The addition of THF effectively improves the charge transport and film morphology of the active layer, the fill factor (FF) of the device is increased from 74.20 to 75.91%, and the photoelectric conversion efficiency (PCE) is increased from 16.85 to 17.70%. Further research compared the effects of THF and its derivatives and structural analogs on the device performance and explored the effect of THF on the device performance of different material systems, and the results show that volatile solvent additives have certain generality in improving film morphology. Our results indicate that the selection of volatile solvents as solvent additives is a promising strategy that can effectively improve the performance of OSCs.

Additive-assisted strategy for high-efficiency organic solar cells

“…Several volatile solvent additives were reported in nonfullerene-based systems recently. 85,86 Tao et al utilized tetrahydrofuran (THF, 66 °C, Fig. 1b) as the additive in D18-Cl:Y6 (Fig.…”

“…2) based OSCs and obtained a higher PCE of 17.70% than the control device without THF (16.85%) (Table 2). 85 According to the TEM and AFM results, THF can improve the morphology of the active layer with enhanced phase separation and a smoother surface, leading to more efficient charge carrier transport and charge collection. Using the space charge limited current (SCLC) method, they confirmed that higher and more balanced charge carrier mobilities were achieved in the device with THF, thus increasing the J SC from 26.20 mA cm −2 to 27.02 mA cm −2 .…”

Unveiling the significance of adduct formation between thiocarbonyl Lewis donors and diiodine for the structural organization of rhodanine-based small molecule semiconductors

“…These additives have a higher boiling point as compared to the main solvent, leading to a slower evaporation rate during the film preparation, thus allowing for fine-tuning of the film crystallinity, as well as the phase separation in the case of blends. 15,22–25…”

“…These additives have a higher boiling point as compared to the main solvent, leading to a slower evaporation rate during the film preparation, thus allowing for fine-tuning of the film crystallinity, as well as the phase separation in the case of blends. 15,[22][23][24][25] The second category, solid additives, operates distinctively from their solvent counterparts, first because they alter the intermolecular interaction among p-conjugated compounds, and second because they are incorporated into the films, so in principle they do not require high temperature for their removal. [26][27][28] Such a scenario is particularly interesting as it avoids the risk of film degradation which inevitably leads to a reduction in device performance.…”