Conjugated Polymer–Small Molecule Alloy Leads to High Efficient Ternary Organic Solar Cells

Abstract

Ternary organic solar cells are promising candidates for bulk heterojunction solar cells; however, improving the power conversion efficiency (PCE) is quite challenging because the ternary system is complicated on phase separation behavior. In this study, a ternary organic solar cell (OSC) with two donors, including one polymer (PTB7-Th), one small molecule (p-DTS(FBTTH2)2), and one acceptor (PC71BM), is fabricated. We propose the two donors in the ternary blend forms an alloy. A notable averaged PCE of 10.5% for ternary OSC is obtained due to the improvement of the fill factor (FF) and the short-circuit current density (J(sc)), and the open-circuit voltage (V(oc)) does not pin to the smaller V(oc) of the corresponding binary blends. A highly ordered face-on orientation of polymer molecules is obtained due to the formation of an alloy structure, which facilitates the enhancement of charge separation and transport and the reduction of charge recombination. This work indicates that a high crystallinity and the face-on orientation of polymers could be obtained by forming alloy with two miscible donors, thus paving a way to largely enhance the PCE of OSCs by using the ternary blend strategy.

Reducing the efficiency–stability–cost gap of organic photovoltaics with highly efficient and stable small molecule acceptor ternary solar cells

“…[1][2][3][4][5] However, the commercialization of OPV requires the availability of inexpensive materials in large quantities such as poly(3-hexylthiophene) (P3HT). P3HT is readily scalable via flow or micro-reactor synthesis, even using 'green' solvents, whilst retaining a high degree of control over molecular weight and regioregularity.…”

“…3,4,[19][20][21][22][23]24 However, simultaneous increase in the Voc, Jsc and FF is a challenge in the ternary approach because of the trade-off between photocurrent and voltage. 23,25,26 Reports show ternary blends using fullerene acceptors, where the Voc is increased using a second acceptor (A2) with a higher electron affinity (EA) than A1; 23,27-29 however, very few examples of two-acceptor ternary blend devices could surpass the overall efficiency of their respective binary blends.…”

Perspective of a new trend in organic photovoltaic: ternary blend polymer solar cells

“…Therefore, ternary PSCs fabricated by using two miscible donors-one is a high-performance polymer and the other is a high-crystalline small molecule-may form alloy and increase the crystallinity simultaneously, which will potentially yield high efficiency ternary PSC. Wei's group [14] incorporated a high crystallinity small molecule 7, 7-(4, 2 ) into a host binary blend of PTB7-Th:PC 71 BM. Both the crystallinity and the face-on preferential orientation with respect to the substrate are enhanced when the small molecule is added, thus resulting in an average PCE of 10.5% by adding a 15% weight ratio of p-DTS(FBTTH2) 2 which is much higher than the binary system based on PTB7-Th:PC 71 BM (an average PCE of 9.2%).…”

“…However, the fabrication process of tandem solar cells is complicate, leading to an increased cost and a decreased yield, which is in contrast to the attractive simplicity of the single-step solution processing for inexpensive solar cells. In recent years, ternary blend PSCs have been explored as an effective strategy to extend light absorption and improve light harvesting, resulting in higher short circuit current densities (J sc ) and higher PCE in a single junction [14,15]. This strategy integrates both the enhanced photon harvesting by incorporating multiple organic materials like in tandem solar cells and simplicity of fabrication process used in single-junction solar cells.…”

Improvement of short circuit current density by intermolecular interaction between polymer backbones for polymer solar cells

“…In addition, most of the OPVs exhibit anisotropic charge transport where the charge moves effectively from the π-stacking direction. 16 Benzo-[1,2-b:4,5-b′]dithiophene (BDT) is one of the donor units of these D-A-type polymers, and it is electron rich because both sides are fused with thiopnenes, the electron-donating units that are resistant to benzene. BDT has been used in a number of OPV studies because of its long QUOTE conjugation length and high planarity.…”