Publication date: 23rd October 2020
Organic solar cells (OSCs) based on donor conjugated polymers and fullerene or non-fullerene acceptors have attracted a considerable attention because of their several unique characteristics such as lightweight, semitransparency, low cost, and simple solution processing.[1] Numerous conjugated polymers with advanced functional properties have been already developed to improve the performance of OSCs. We recently proposed and implemented an approach to design of novel conjugated polymers with an extended system of alternating donor and acceptor blocks (X-DADAD)n.[2] The first (X-DADAD)n-type polymer composed of carbazole, thiophene and benzothiadiazole units (PCbz) showed improved optoelectronic properties in comparison with well known (X-DAD)n analogues. However, low solubility of PCbz resulted in poor film quality and low efficiencies (<1%) of OSCs based in this material.
In this work, we modified the structure of previously reported conjugated polymer PCbz by replacing the carbazole block with phenylene fragment bearing two bulky 2-octyldodecyloxy side chains and introducing fluorine into the benzothiadiazole acceptor blocks. As result, two novel low-bandgap conjugated polymers P1 and P2 with improved physicochemical and optoelectronic properties were synthesized (Fig.1). Both polymers exhibited good solubility in organic solvents. The introduction of fluorine atoms in P2 decreased its HOMO energy to -5.6 eV that is beneficial for achieving high open-circuit voltages in organic solar cells.
Fig.1 Structure of conjugated polymers PCbz, P1, P2, and J−V curves of OSCs based on their polymers.
Both novel polymers were investigated as electron-donor materials in OSCs with fullerene derivative [70]PCBM as the acceptor component. The OSCs based on fluorine-containing polymer P2 showed considerably improved photovoltaic performance compared to the devices assembled using P1 or PCbz polymers. In particular, the power conversion efficiency of OSCs based on Р2/[70]PCBM blends reached ⁓7%, which is a decent result for fullerene-based organic photovoltaics. Further improvement in the efficiency of OSCs might be reached using state-of-the-art non-fullerene acceptors.
This work was supported by the Russian Foundation for Basic Research (grant No. 20-03-00309).
General support was also provided by the Ministry of Science and Higher Education of the Russian Federation within the project No. AAA-A19-119071190044-3 (0089-
2019-0010)
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