Two easily accessible π-conjugated pyrene sulfonates, 1-pyrenesulfonic acid sodium salt (PyS) and 1,3,6,8-pyrenetetrasulfonic acid tetrasodium salt (PyTS), as cathode interfacial layers (CILs) for polymer solar cells (PSCs) are demonstrated. The two interlayer materials, with polar sulfonates directly linking to a conjugated unit, are quite different from other kinds of interfacial materials with functional groups attached to non-conjugated alkyl chains. Moreover, the two molecules show distinct intramolecular dipoles. PyS with a strong permanent dipole moment can reduce the work function of the bulk-heterojunction (BHJ) films, while centrosymmetric PyTS with no overall dipole has little effect on the work function of BHJ films. It is also found that PyS based devices show much improved charge transport ability and conductivity than those based on PyTS. As a result, PyS based devices exhibit a high power conversion efficiency (PCE) of 7.46% for the PBDTTT-C:PC71BM system, while PyTS based devices show a relatively low PCE of 6.28%. A higher efficiency of 8.82% is achieved for PTB7-Th as the donor. In addition, benefitting from the planar structure of the pyrene units, PyS with high conductivity can function efficiently in a wide thickness range of 2 to 41 nm.

In recent years, a large library of n-type polymers have been developed and widely used as acceptor materials to replace fullerene derivatives in polymer solar cells (PSCs), stimulating the rapid expansion of research on so-called all-polymer solar cells (aPSCs). In particular, rylene diimide-based n-type polymer acceptors have attracted broad research interest due to their high electron mobility, suitable energy levels, and strong light-harvesting ability in the visible region. Among various polymer acceptors, rylene diimide-based polymers presented best performances when served as the acceptor materials in aPSCs. Typically, a record power conversion efficiency (PCE) of 7.7% was very recently achieved from an aPSC with a rylene diimide polymer derivative as the acceptor component. In this review, we highlight recent progress of n-type polymers originated from two significant classes of rylene diimide units, namely naphthalene diimide (NDI) and perylene diimide (PDI), as well as their derivatives for aPSC applications.Sustained research attention has been put on all-polymer solar cells (aPSCs) in recent years. This critical review highlights the latest progress in rylene diimide-based polymers as acceptors in aPSCs.Download high-res image (183KB)Download full-size image

Two easily accessible π-conjugated pyrene sulfonates, 1-pyrenesulfonic acid sodium salt (PyS) and 1,3,6,8-pyrenetetrasulfonic acid tetrasodium salt (PyTS), as cathode interfacial layers (CILs) for polymer solar cells (PSCs) are demonstrated. The two interlayer materials, with polar sulfonates directly linking to a conjugated unit, are quite different from other kinds of interfacial materials with functional groups attached to non-conjugated alkyl chains. Moreover, the two molecules show distinct intramolecular dipoles. PyS with a strong permanent dipole moment can reduce the work function of the bulk-heterojunction (BHJ) films, while centrosymmetric PyTS with no overall dipole has little effect on the work function of BHJ films. It is also found that PyS based devices show much improved charge transport ability and conductivity than those based on PyTS. As a result, PyS based devices exhibit a high power conversion efficiency (PCE) of 7.46% for the PBDTTT-C:PC71BM system, while PyTS based devices show a relatively low PCE of 6.28%. A higher efficiency of 8.82% is achieved for PTB7-Th as the donor. In addition, benefitting from the planar structure of the pyrene units, PyS with high conductivity can function efficiently in a wide thickness range of 2 to 41 nm.