Perovskite solar cell with copper electrode hits 20.1% efficiency

Scientists from the Beijing Institute of Technology have developed a solar cell with a back electrode made of copper (Cu) instead of silver (Ag) or gold (Au).

“Cu as an earth-abundant element is the promising candidate to be an electrode for its comparable physical properties with Au and Ag and exhibits good stability with simultaneously low cost,” the research group said. “It costs less than 1/80th that of Ag and 1/5,500th that of Au” Zhou said. “Cu is the promising candidate to be PSC electrode for its comparable physical properties (i.e. conductivity) with Au and Ag, and good stability.”

The solar cell has a planar n-i-p structure and consists of an indium tin oxide (ITO) substrate, tin(IV) oxide (SnO2) buffer layer, a perovskite layer, a hole transport layer (HTL), and a layer made of copper. The researchers adjusted the fermi level of the HTL to match both the perovskite and the Cu electrode. They used a solution based on poly(triaryl)amine (PTAA), which is a hole-transporting and electron-blocking material, as well as a Spiro-OMeTAD precursor. The fermi level is the maximum kinetic energy of an electron at 0 Kelvin.

In the proposed HTL configuration, the energy difference at the HTL/Cu interface can be reduced to improve carrier transportation.

“Just like the buckets effect, we hope both perovskite/HTL and HTL/Cu interfaces are not the shortest buckets during device operation,” said the researchers. “The balanced energy difference between perovskite/HTL and HTL/Cu interfaces could significantly improve the charge collection and transport properties in the resultant n-i-p perovskite solar cell devices.”

Under standard illumination conditions, the cell achieved a power conversion efficiency of 20.10%, an open-circuit voltage of 1.084 V, and a fill factor of 78.77%, which the research team describes as the highest efficiency ever achieved in n-i-p solar cells with Cu electrode. The device was also able to retain 92% of its initial efficiency after 1,000 hours.

“This finding not only extends the understanding on the band alignment of neighboring semiconductor functional layer in the device architecture to improve the resulting performance, but also suggests great potential of Cu electrode for application in PSCs community,” the academics said.

They presented their work in “Balancing Energy-Level Difference for Efficient n-i-p Perovskite Solar Cells with Cu Electrode,” which was recently published in Energy Material Advances.

“The present work not only expanded our knowledge on seeking a balanced band alignment at different interfaces to improve the performance of devices but also ensured the application of Cu electrode in further perovskite solar cell industrialization,” they concluded.