Comparing C60 and C70 as acceptor in organic solar cells: Influence of the electronic structure and aggregation size on the photovoltaic characteristics

Abstract

The difference in aggregation size of the C 60 and C 70 fullerenes affect the photovoltaic performance of devices assembled in the so-called bilayer architecture with poly[2,7-(9,9-dioctyl-dibenzosilole)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole] (PSiF-DBT) as the electron donor material. Despite the better performance of the C 70 devices, which is related to the high absorption coefficient in the visible range and the superior charge transport properties, the short-circuit current variation upon annealing treatment at 100°C is approximately twice bigger when the C 60 is the acceptor. We attribute this effect to the tendency of C 60 in form smaller aggregate domains relatively to the C 70. The increased roughness on the polymeric surface after annealing results in an enhanced donor/acceptor contact area and assists the fullerene diffusion deeper inside the polymeric layer. This effect leads to a better mixing between donor and acceptor species and create a interpenetrating layer close to the so-called bulk heterojunction. Since C 60 forms smaller aggregates, this mechanism is more pronounced for this molecule. Therefore, a significant variation in the performance of the C 60 devices is observed after this kind of treatment. Density Functional Theory calculations of the potential energy of interaction between two fullerene molecules and X-Ray measurements gives evidences to support this idea. In addition, combining spectrally resolved external quantum efficiency measurements with optical modeling our results also indicate the occurrence of the bilayer interfacial mixing for PSiF-DBT/C 60 .

New Fullerene Derivative as an n‐Type Material for Highly Efficient, Flexible Perovskite Solar Cells of a p‐i‐n Configuration

“…If only the electronic contributions were considered, it would give the opposite result (ΔE of 0.12 and 0.21 eV for PCBM and PCBC6, respectively). The higher aggregation tendency calculated for PCBC6 with respect to PCBM we associate with a tendency to form more uniform, smoother and more stable film, due to the stronger intermolecular dispersion interactions that optimize, as it was proposed by Benetto et al [33] (Insert Figure 2…”

“…The higher aggregation tendency calculated for PCBC6 with respect to PCBM we associate with a tendency to form more uniform, smoother, and more stable film, due to the stronger intermolecular dispersion interactions that optimize its growth, as it was proposed by Benetto et al. [ 33 ]…”

“…If only the electronic contributions were considered, it would give the opposite result (ΔE of 0.12 and 0.21 eV for PCBM and PCBC6, respectively). The higher aggregation tendency calculated for PCBC6 with respect to PCBM we associate with a tendency to form more uniform, smoother, and more stable film, due to the stronger intermolecular dispersion interactions that optimize its growth, as it was proposed by Benetto et al [33] Having established a rational interpretation of the different film morphologies for the investigated molecules, we move to analyze the electronic properties of both ETMs. The role of an ETM in perovskite solar cells is to extract photogenerated electrons and reflect holes.…”

Naphthalocyanine-Based NIR Organic Photodiode: Understanding the Role of Different Types of Fullerenes

“…Figure 2a also shows that PC 71 BM has a stronger and broader absorption range in the visible spectrum compared to PC 61 BM. The less symmetrical structure of PC 71 BM helps to relax the forbidden transitions in longer wavelengths and increases light absorption compared to PC 61 BM [22,23]. can be inferred that blends with PC71BM have a stronger absorption in the visible range compared to the blend with PC61BM.…”

“…The presence of clusters might increase the surface roughness values. According to L. Benatto et al (2020), high surface roughness can enhance the donor-acceptor contact area and assist the charge carrier diffusion in the interpenetrating layer [23]. Besides, the n-types used in the blended film also affect the surface roughness values.…”