Ultrathin HfAlO ferroelectrics enhancing electron transport and perovskite solar cell performance

Ferroelectric materials are promising for solar energy conversion due to the unique spontaneous polarization effect, leading to effective control of electron-hole recombination and potentially high power conversion efficiency of perovskite solar cells. Herein, the ultrathin ferroelectric hafnia alumina (HfAlO) films were obtained by atomic layer deposition and applied to modify the electron transport layer of PSCs. The XPS and AFM characterizations indicate that the Hf0.39Al0.10O films feature smooth, dense, and compact surface morphology. For the devices incorporating the ultrathin HfAlO films, the oriented ferroelectric effect-induced spontaneous polarization and internal electric field are crucial factors to enhance the charge separation during charge transfer. Accordingly, the short circuit current, open-circuit voltage, and power conversion efficiency (PCE) are increased by 11.8%, 9.0%, and 29.8%, respectively. Moreover, the HfAlO incorporating devices retained ~ 80% of the original PCE after 500 h ageing, much better than that of the pristine devices showing the retention of only ~ 50% of the original PCE.