Silicon Heterojunction Solar Cells Using Thermally -Evaporated Molybdenum Oxides As Dopant-Free Hole Selective Contact

Dopant-free carrier selective contacts have garnered significant interest for the development of high-efficiency silicon solar cells due to their low-temperature processing and suppression of free-carrier absorption. In this work, we investigate thermally-evaporated molybdenum oxides (MoOx) functioning as a hole-selective contact (HSC) for silicon heterojunction (Si HJT) solar cells. The high work function of MoOx results in upward energy band bending at the MoOx/n-type Si interface, which facilitates the hole transport and blocks the electron. We compare the optical properties of MoOx with different thickness settings of 3, 10, and 15 nm, where the optical bandgap is fitted via the tauc plot and ranging between 3.46, 3.44, and 3.42 eV, respectively. The absorption spectra of MoOx, MoOx with an intrinsic amorphous silicon (a-Si(i)) layer, and sputtered tin-doped indium oxides (ITO) are also presented. The transmission electron microscopy further reveals a 2.8nm-thick silicon oxides layer in between the MoOx and silicon interface. Preliminary results show that the Si HJT cell with a 15 nm-thick MoOx layer achieves a power conversion efficiency (PCE) of 20.3% and an open-circuit voltage (Voc) of 651.9mV, possibly limited by the pyramidal surface morphology and the a-Si(i) interface passivation layer.