A group of scientists based in China and the United States has utilized polymer zwitterions that incorporate conjugated units to modify zinc oxide interlayers in organic solar cells.
Their work is presented in the research paper “Modification of zinc oxide interlayers with naphthalene diimide-based polymer zwitterions for efficient organic solar cells,” available in the journal Wearable Electronics.
The study’s senior author, Yao Liu, explained that zinc oxide films often contain numerous defects that act as electron traps and recombination centers, degrading device performance. “To address this, metals, organic molecules and polymers have been introduced into zinc oxide films for defect passivation and modification,” Liu said.
The research team designed two novel polymer zwitterions, with benzene rings (BZ) or C=C double bonds (CZ), by integrating naphthalene diimide conjugated units and sulfobetaine zwitterion pendant groups.
The researchers found that the zwitterionic components effectively passivate zinc oxide defects, helping to improve electrical properties while adjusting the energy level to facilitate more efficient charge extraction. Meanwhile, the ultraviolet light absorption properties of the naphthalene diimide units were found to protect the active layers from photodegradation.
When implemented into an organic solar cell, the BZ- and CZ-modified zinc oxide films demonstrated a power conversion efficiency of 17.96% and 17.97% respectively.
“These results confirm that the polymer zwitterions effectively enhanced the performance of the zinc oxide nanoparticle electron transport layers, with significant improvements in device efficiency,” the research paper says, while adding that the films also demonstrated substantially improved device stability.
The paper concludes that polymer zwitterion modification is a promising strategy for developing high-performance metal oxide transport layers in organic photovoltaics. “Polymer zwitterion-modified zinc oxide is a promising material candidate for flexible and wearable electronics, uniquely combining mechanical durability with stable electrical performance,” Liu added.
The research team consisted of scientists based at Beijing University of Chemical Technology and the University of Massachusetts Amherst.
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