Understanding the Impact of Hierarchical Nanostructure in Ternary Organic Solar Cells

Abstract

Ternary organic solar cells (OSCs), which blend two donors and fullerene derivatives with different absorption ranges, are a promising potential strategy for high‐power conversion efficiencies (PCEs). In this study, inverted ternary OSCs are fabricated by blending a highly crystalline small molecule BDT‐3T‐CNCOO in a low band gap polymer PBDTTT‐C‐T:PC71BM. As the small molecule is introduced, the overall PCEs increase from 7.60% to 8.58%. The morphologies of ternary blends are studied by combining transmission electron microscopy and X‐ray scattering techniques at different length scales. Hierarchical phase separation is revealed in the ternary blend, which is composed of domains with sizes of ≈88, ≈50, and ≈20 nm, respectively. The hierarchical phase separation balances the charge separation and transport in ternary OSCs. As a result, the fill factors of the devices significantly improve from 58.4% to 71.6%. Thus, ternary blends show higher hole mobility and higher fill factor than binary blends, which demonstrates a facile strategy to increase the performance of OSCs.

Combining Energy Transfer and Optimized Morphology for Highly Efficient Ternary Polymer Solar Cells

“…[9][10][11][12][13] Therefore, compared with the corresponding binary systems, TSCs have the potential to achieve higher light-harvesting and/or improved charge transport, leading to increased J sc and/or FF. [14][15][16] However, it should be noted that the emission of the third component and the absorption of the donor or acceptor must overlap in order to get efficient energy transfer. In addition, the morphology tuning highly depends on the crystallinity and miscibility properties of the materials involved.…”

Recent Advances in Morphology Optimization for Organic Photovoltaics

“…The resulting changes in film morphology, i.e., high crystallinity and appropriate phase separation, boosted the PCE from 6.85% to 8.40%. Similar phenomena were observed when BDT‐3T‐CNCOO was added to a PBDTTT‐C‐T:PC 70 BM blend: the domain size and purity are increased when 50% BDT‐3T‐CNCOO is incorporated; moreover, the presence of BDT‐3T‐CNCOO induces the formation of nanofibrous polymer domains that facilitate charge transport . Huang et al incorporated 2,4‐bis[4‐( N , N ‐diisobutylamino)‐2,6‐dihydroxyphenyl] squaraine (SQ) into a P3HT:PC 60 BM blend and found that it broadens the spectral absorption and induces the formation of a nanomorphology .…”

Toward Over 15% Power Conversion Efficiency for Organic Solar Cells: Current Status and Perspectives

“…Generally, a ternary blend has one additional electron donor or acceptor material compared with its binary counterpart. In addition to complementary absorption with respect to the binary blend, the third component also plays a very important role in tuning the morphology of the active layer though molecular interactions between the donors and acceptors, resulting in pure domains, face‐on orientations, and higher crystallinity, which are beneficial for exciton dissociation and charge transport . As a consequence, the J sc and FF are improved for ternary OSCs.…”