Even if they did not provide the same level of performances in OSCs as fullerene-based devices, the use of n-type polymers is of great interest owing to the possibility of tuning their optoelectronic properties to optimize their light-harvesting capability and improve their stability. In this context, a variety of D-A acceptor polymers based on benzothiadiazole (BT), dithienodiketopyrrolo pyrrole (DPP), thienopyrroledione (TPD), naphthalene diimide (NDI), and perylene diimide (PDI) have been developed. With the need of reducing more and more the bandgap, n-type polymers exhibiting a LUMO level at −4 eV have been tested for integration in organic field-effect transistors (OFETs) and OSCs. However, since fullerene derivatives suffer from limitations like weak absorption and low stability due to dimerization (burn-in) and unstable morphology, non fullerene acceptors (NFAs) were developed for organic electronic devices. Generally, D-A copolymers were mainly used as donor materials (p-type) combined with fullerene acceptors (n-type) for organic solar cells (OSCs). The vast majority of conjugated polymers dedicated to organic electronics are developed using the donor-acceptor (D-A) strategy, which consists of combining electron-rich (D) and electron-poor (A) units, and in varying their nature through chemical design in order to finely tune their bandgap. By comparing A-A’ to D-A’ copolymers analogues, it was shown that the bandgap remained the same while both HOMO and LUMO levels were lowered by roughly 0.2 eV. These results were compared to analogous donor-acceptor (D-A) copolymers previously reported, in which DPP is replaced by DTS, P(DTS-DPP), P(DTS-DAP), and P(DTS-BTPBF). The BTPBF unit allowed a strong reduction of the bandgap, leading to a broad absorption in the visible and near infra-red regions from 650 to 1450 nm. UV-visible spectrophotometry and cyclic voltammetry were used to estimate the optical and electrochemical bandgaps, and were found as very small: 1.3, 1.0, and 0.9 eV for P(DPP-DPP), P(DPP-DAP), and P(DPP-BTPBF), respectively. The experimental and computed optoelectronic properties of four DPP-based copolymers, P(DPP-DPP) (with linear and branched chains), copolymer with diazapentalene P(DPP-DAP) and also with dioxothienopyrrolebenzodifurandione P(DPP-BTPBF), as well as thermal characterizations were described.
#LUMO VS HOMO SERIES#
A series of acceptor-acceptor (A-A’) alternated copolymers based on dithienodiketopyrrolo pyrrole were synthesized by copolymerizing it with itself and other different electron-poor monomers.
0 kommentar(er)
