A novel full-area dopant-free cesium iodide (CsI, approximately 3 nm thick) serves as an electron-selective and passivation contact for crystalline silicon (c-Si) solar cells, achieving a champion power conversion efficiency of 21.75%. Thermally evaporated CsI films on n-Si exhibits ohmic contacts (3 mΩ·cm2), passivation properties (Δn = 1.0×1015 cm-3, τ
eff of ≈ 265 μs) and stable contact properties below 300°C.
Dopant-free carrier-selective contacts have the potential to overcome parasitic absorption and doping-related recombination associated with heavy doping. It offers a simpler preparation process and low-temperature fabrication, which has attracted considerable research interest. This study demonstrated a novel full-area dopant-free cesium iodide (CsI, approximately 3 nm thick) as an electron-selective and passivation contact for crystalline silicon (c-Si) solar cells via thermal evaporation, achieving a champion power conversion efficiency of 21.75%. Desired Ohmic contacts, with contact resistivity around 3 mΩ·cm2, are formed between lightly doped n-type c-Si and metal electrodes (such as Ag, Al, and Mg) by inserting nanoscale CsI films. CsI film exhibits surprising insensitivity when in contact with the metal electrode. Furthermore, it is found that the thermal evaporation deposition CsI on n-Si exhibits passivation properties at their interface due to the field passivation of n+-n junctions and the chemical passivation of Si-I bonds. Additionally, the stability of CsI is enhanced through thermal annealing, maintaining the stability of contact properties below 300°C. The CsI film offers a dual effect of selective carrier transport and reduced recombination, which simplifies the production process and expands the application of cesium-based materials in photovoltaic devices.
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