Novel Passivating Contacts for Silicon Photovoltaics

Carrier selective passivating contacts, which provide dual functions of surface defect passivation and extracting one type of charge carriers, attract attention for realizing high efficiency crystalline silicon solar cells. Hydrogenated amorphous silicon (a-Si:H) has been a key enabler known as the silicon heterojunction (SHJ) technology. Here we pursued novel materials focusing on hole-selective passivating contacts: one is the hydrogenated nanocrystalline silicon (nc-Si:H) and the other is the metal-oxide (non-silicon) material. For the nc-Si:H, it is demonstrated that the use of the $(p)\text{nc-Si:H}/(i)\text{a-Si:H}$ stack instead of the conventional $(p)\text{a-Si:H}/(i)\text{a-Si:H}$ in SHJ solar cells provides not only a mitigation of the parasitic absorption loss but also improvements in passivation and electrical contact properties. This results in an efficiency increase by 0.3-0.6% absolute compared to our reference cell, and a best cell efficiency of 23.5%. For metal-oxide material, we have developed an atomic-layer-deposited titanium oxide ($\text{TiO}_{\mathrm{x}}$) that functions as an efficient and transparent hole-selective passivating contact without using buffer layer, leading to the proof-of-concept solar cells with efficiencies above 20%.