Researchers at South Korea’s Ulsan National Institute of Science and Technology (UNIST) have used organic p‐type hole transport materials to increase the efficiency of colloidal quantum dot solar cells.
They created a 12.82%-efficient organic hybrid series tandem photovoltaic device combining quantum dots and organic bulk heterojunction (BHJ) photoactive materials. They claimed that this efficiency rate is the highest among the reported colloidal quantum dot cells, including single-junction devices and tandem devices.
The research team used sulfur‐exchanged quantum dot ink instead of solid‐state ligand exchange (SSE) to produce the cells. Ligand exchange – a chemical reaction in which a ligand in a compound is replaced by another – is used in quantum dot cells to improve charge carrier mobility and reduce defects on the surface. The researchers replaced the SSEs with the ink and demonstrated that their performance is comparable, with the advantage of avoiding a manufacturing step.
The hole transport materials were made with π‐conjugated polymers, as their conductivity can be changed from a semiconducting state to a metallic p-doping state. “The entire device fabrication was executed without using either SSE or Layer-by-Layer process, which will be advantageous for exploiting commercial processing techniques,” the scientists said.
They added that the hybrid tandem device showed almost negligible degradation after air storage for three months. “This study suggested the potential to achieve a power conversion efficiency over 15% in hybrid tandem devices by reduction of energy loss in CQDPVs and enhancement of NIR absorption in OPVs,” said researcher Sung-Yeon Jang.