Quantum dot hybrid HTJ cell with 12.82% efficiency

Scientists from South Korea’s Ulsan National Institute of Science and Technology (UNIST) have developed hybrid tandem solar cells with quantum dots and organic bulk heterojunction (BHJ) photoactive materials, for which they claim to have achieved a conversion efficiency of 12.82%.

This efficiency level is among the highest recorded for single-junction and tandem devices, the research team claimed, while adding that the rate was achieved by optimizing the short-circuit current density balance of each sub‐cell. The achieved efficiency is also higher than that of each single-junction device, which is 11.17% for the quantum dot device and 11.02% for the organic BHJ device.

They said that the organic bulk heterojunction photoactive materials with which the cell was hybridized are designed to compensate for the external quantum efficiency (EQE) loss in the near-infrared (NIR) region. “The NIR-absorbing organic BHJ devices were employed as the back sub-cells to harvest the transmitted NIR photons from the CQD front sub-cells,” they explained.

Although quantum dots are good at absorbing light in the NIR, they may not be able to absorb light in all of the cell areas, the researchers said.

“This study suggests a potential route to improve the performance of CQDPVs by proper hybridization with NIR-absorbing photoactive materials,” they said, noting that they are convinced that the new cell could reach an efficiency rate of around 15% if they continue to reduce energy loss in the quantum dot cell and enhance NIR absorption.

The research team manufactured the cell through a simple production process and at room temperature. It exhibited almost negligible degradation after air storage for three months, they noted. The cell is described in the study Efficient Hybrid Tandem Solar Cells Based on Optical Reinforcement of Colloidal Quantum Dots with Organic Bulk Heterojunctions, published in Advanced Energy Materials.