Dry Transfer Printed Hole Transport Layer for Hysteresis-Free Colloidal Quantum Dot Solar Cells

Colloidal quantum dot (CQD) solar cells have drawn a lot of attention because of their potential for bandgap engineering, which enables broad and powerful absorption in the wavelength of sunlight, and low-cost process based on the solution phase production. However, the interfacial problems resulting from the heterojunction structure containing electron and hole transport layers cause a hysteresis phenomenon that weakens the device stability. We used the dry-transfer technique to implement a hole transport layer (HTL) with enhanced interfacial properties in devices. This approach is highly reproducible and allows for precise thickness control of the HTL. It also uses substantially less environmentally harmful organic solvents for the ligand exchange process than those required by the previous layer-by-layer (LbL) deposition technique. Additionally, about 400 nm thick CQD film could be deposited without the ligand exchange process, and a power conversion efficiency of 10% with minimized hysteresis was achieved using this method. Moreover, by improving the interfacial properties over the traditional LbL approach, it was feasible to lower the charge transfer resistance related to the device's hysteresis by a factor of up to four or more.