Researchers have started to focus on colloidal quantum dot (CQD) solar cells, mainly because of their advantages of being adaptable and weightless. Moreover, they are incredibly easy to produce, in comparison with commercial silicon solar cells currently being used.
A new technology, able to maximize the performance of the existing CQD solar cells, has recently been created. A team of researchers led by Professor Sung-Yeon Jang at the School of Energy and Chemical Engineering at UNIST in South Korea has managed to create high-effective, solution-processed, hybrid series, tandem photovoltaic devices packing CQD solar cells and organic heterojunction (BHJ) photoactive materials.
The organic back cell absorption efficiently reimbursed the optical loss in the CQD front cell, which enhanced the overall photon harvesting.
Quantum dots (QDs) are semiconductor particles with masses smaller than a few nanometers. As they showcase intriguing phenomena, such as size reliant emission wavelength, the absorption spectrum of the solar cell can be rather changeable. Simply put, the advantage of QDs is that it depicts light absorption in the near-infrared (NIR) area, which other photoactive sheets are not able to do. Still, there are some places in the NIR region where light absorption doesn’t happen, even with QDs.
In the research, scientists created high-efficiency CQD, or organic hybrid series along with photovoltaic devices, displaying CQDs and organic BHJs as photoactive materials to pay for the external quantum efficiency (EQE) loss in the NIR area.
The NIR-absorbing organic BHJ devices were applied as the back sub-cells to reap the transmitted NIR photons from the CQD front sub-cells.
The Highest Amount Among CQDPVs
Moreover, the researchers adjusted the short-circuit current density balance of each sub-cell, therefore, creating a close to ideal series connection utilizing a medium layer to reach a power conversion efficiency (PCE) that is above that of each single-junction device.
The PCE – 12.82 percent – of the hybrid tandem device was the greatest among the reported CQDPVs, as well as single-junction devices and tandem devices, as per the team of scientists. In addition, the researchers also said that this study ‘suggests a potential route to improve the performance of CQDPVs by proper hybridization with NIR-absorbing photoactive materials.’
“The hybrid tandem device exhibited almost negligible degradation after air storage for three months,” says Professor Jang. “Moreover, this study suggested the potential to achieve PCE > 15 percent in hybrid tandem devices by reduction of energy loss in CQDPVs and enhancement of NIR absorption in OPVs.”
The discoveries have been published in the journal Advanced Energy Materials on January 13th, 2020.