Low-temperature synthesis of conducting boron-doped nanocrystalline silicon oxide thin films as the window layer of solar cells

Low-temperature synthesis of highly transparent conducting B-doped (p-type) nc-SiO_X:H films has been pursued by 13.56 MHz plasma-CVD, using a combination of SiH₄, CO₂ and B₂H₆, diluted by H₂ and He. Higher substrate temperature (T_S) encourages nanocrystallization in B-doped nc-SiO_X:H network by reducing bonded H-content, while bonded O-content also reduces simultaneously. At optimized T_S = 150 °C, p–nc-SiO_X:H film having an optical band gap ~1.98 eV, high conductivity ~0.18 S cm⁻¹, has been obtained via dopant-induced escalation of the electrically active carriers at a deposition rate ~5.3 nm/min. The p–nc-SiO_X:H film appears as a promising window layer for the top sub-cell of multi-junction silicon solar cells. A single-junction nc-Si:H based p-i-n solar cell of efficiency (η) ~7.14% with a current-density (J_SC) ~14.18 mA/cm², reasonable fill-factor (FF) ~66.2% and open-circuit voltage (V_OC) ~0.7606 V has been fabricated, using the optimum p-type nc-SiO_X:H as the window layer deposited at T_S = 150 °C.