Dopant-Free Bifacial Silicon Solar Cells

Herein, challenges in the fabrication of full dopant-free bifacial silicon solar cells are discussed and efficient devices utilizing a MoO3/ indium tin oxide (ITO)/Ag hole-selective contact and ZnO/LiFx/Al electron-selective contacts with up to 79% short-circuit current bifaciality are demonstrated. The ZnO/LiFx/Al rear electron contact features a full-area ZnO antireflective coating and a LiFx/Al finger contact, allowing sunlight absorption from the back side, thus producing more overall power. The ZnO/LiFx/Al electron contacts with a thinner ZnO layer and a larger contact fraction display a better selectivity and a lower resistance loss. When considering rear-side irradiance of 0.15 sun, the dopant-free bifacial solar cell with 60 nm ZnO and 50% LiFx/Al metal contact fraction achieves a 3% estimated output power density improvement compared with its monofacial counterpart (21.0 mW cm(2) compared to 20.3 mW cm(2)) using the full-area back contact. Both the efficiency and bifaciality factor of this dopant-free device are still significantly lower than those of state-of-the-art devices relying on doped-silicon-based layers. The required improvement for this technology to become industry-relevant is discussed.