Eliminating the excess energetic driving force in organic solar cells leads to a smaller energy loss and higher device performance; hence, it is vital to understand the relation between the interfacial energetics and the photoelectric conversion efficiency. In this study, we systematically investigate 16 combinations of four donor polymers and four acceptors in planar heterojunction. The charge generation efficiency and its electric field dependence correlate with the energy difference between the singlet excited state and the interfacial charge transfer state. The threshold energy difference is 0.2 to 0.3 eV, below which the efficiency starts dropping and the charge generation becomes electric field-dependent. In contrast, the charge generation efficiency does not correlate with the energy difference between the charge transfer and the charge-separated states, indicating that the binding of the charge pairs in the charge transfer state is not the determining factor for the charge generation.
This Review aims at a comprehensive overview on the recent stereospecific control polymerizations by group 3 metal complexes based catalytic systems in combination with aluminum alkyls and organoborates etc. co‐catalysts. The involved monomers include styrene and substituted styrenes, and the conjugated dienes like isoprene and butadiene, and their derivatives. The syndio‐ and iso‐selective polymerizations of styrene, unmasked polar styrenes and the copolymerizations of styrene with conjugated dienes and polar styrenes are summarized. The factors of influencing the catalytic activity and selectivity are discussed. The regio‐ and stereo‐ selective polymerizations of conjugated dienes, polar diene derivatives and their copolymerizations are reviewed. The relationship between catalyst structure and polymerization activity, the mechanism of stereo‐selective polymerization and the influence of different cocatalysts are discussed.
New donor–acceptor-type copolymers containing
dioxocycloalkene-annelated
thiophenes as electron-accepting units have been designed and synthesized
for application to p-type organic semiconducting materials in organic
photovoltaics. The investigation of their photophysical and electrochemical
properties revealed that these copolymers possessed low optical bandgaps
(from 1.63 to 1.92 eV) and low-lying HOMO energy levels (from −5.41
to −5.33 eV). Organic field-effect transistor measurements
revealed that these copolymers had hole-transporting characteristics
with mobilities on the order of 10–7–10–4 cm2 V–1 s–1. The bulk-heterojunction photovoltaic devices fabricated from blends
of these copolymers with fullerene derivatives as acceptors showed
high power conversion efficiencies of up to 4.87%, with an open-circuit
voltage of 0.90 V, a short-circuit current of 11.46 mA cm–2, and a fill factor of 0.48 under air mass 1.5 simulated solar illumination.
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