Wide‐Bandgap Binary Metal Oxide Electron Transport Layer for Solar Cells

Metal oxides have been developed to replace heavily doped silicon thin film in crystalline silicon (c-Si) solar cells, aiming to reduce parasitic light absorption and simplify manufacturing. However, the performance of these devices is often limited by the conductivity and stability of metal oxides. Herein, a novel electron-selective material-atomic layer deposition (ALD) zinc tin oxide (ZTO) is presented. ZTO thin films exhibit an expanded optical bandgap and high transmission. Due to the high oxygen vacancy concentration and low work function (3.52 eV) of ZTO thin films, the c-Si/ZTO/Al structure achieves ohmic contact characteristics. In addition, by inserting an ultrathin lithium fluoride (LiF) film between ZTO and Al, the contact resistivity can be further reduced to 2.09 mΩ·cm². Implementing SiO_x/ZTO/LiF/Al as electron-selective contacts enable the c-Si solar cell with a PCE of 22.5% and the device demonstrates excellent long-term stability for over 1000 h in air. Therefore, ZTO/LiF/Al exhibits great potential as an excellent electron transport layer for c-Si solar cells. ZTO thin films are also expected to be applied in perovskite solar cells, organic solar cells, and other fields in the future.