All-polymer organic solar cell with 16.05% efficiency


An international group of researchers has developed a layer-by-layer (LbL) processed all-polymer organic solar cell for applications in indoor photovoltaics and building-integrated photovoltaic (BIPV) projects.

“Our device processing method can be prepared in a large area, which will help promote its further commercialization,” the research's corresponding author, Yue Zhang, told pv magazine. The cell was built with a top donor material known as PBDB-T and an electron acceptor made of the polymer PYT. The microstructures of PBDB-T and PYT were processed through LbL processing assisted by solvent additive and thermal annealing.

“By adding a small amount of 1-chloronaphthalene (CN) during the deposition of the top layer (PYT) and applying a post thermal annealing treatment on the PBDB-T/PYT active layer, the lamellar crystalline coherence length (CCL) of PBDB-T was improved significantly, and polymer fibrils were formed in the PYT phase,” the scientists explained. “Besides, BHJ-like morphology with intimate interdiffusion between PBDB-T and PYT in the vertical direction, yet favorable vertical composition distribution, has been formed in the PBDB-T/PYT film.”

According to them, this cell architecture creates the conditions for a longer exciton lifetime, improved exciton dissociation, reduced trap densities and charge recombination losses, as well as more efficient charge transport and extraction.

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Tested under standard radiation conditions, the device achieved an open-circuit voltage of 0.91V, a short-circuit current of 23.07mA/cm2, a fill factor of 0.77, and a power conversion efficiency of 16.05%, which the academics described as the highest efficiency ever reported for an all-polymer solar cell based on polymerized small molecular acceptors (PSMAs).

This study demonstrates an effective strategy to finely regulate the microstructures of the polymer donor and acceptor in allpolymer solar cells,” the academics concluded. “In combination with the intrinsic advantages in controlling vertical composition distribution and phase separation, via LbL processing, these findings suggest broader implications for the efficiency enhancement of allpolymer solar cells.”

The cell was presented in the paper “Layer-by-layer processed binary all-polymer solar cells with efficiency over 16% enabled by finely optimized morphology,” published in Nano Energy. The research group includes scientists from the South China University of Technology, the Friedrich-Alexander-Universität Erlangen-Nürnberg, in Germany, and the Eindhoven University of Technology, in the Netherlands.

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