Substrate temperature has an important role on the characteristic properties of a plasma deposited thin film silicon. In a heterojuction (HJ) solar cell, the higher deposition temperature initiates unwanted thermal diffusion of atom from one layer to another, thereby degrading device characteristics. Hence, we investigated the effect of substrate temperatures (T-s) on p-type material and HJ device characteristics. We prepared p-type nanocrystalline silicon oxide (p-nc-SiO:H) layer at different T-s varying from 170 degrees C to 80 degrees C and observed that its opto-electronic properties improve at a lower T-s. These p-nc-SiO:H were used in HJ solar cell as emitter and we found that the film prepared at 80 degrees C gives the best result. This emitter layer shows wide optical gap (2.32 eV), high electrical conductivity (3.5 S/cm) and high crystallinity (44%). In the rear emitter HJ solar cells, an improvement in fill factor from 72.2% to 74.5%, open circuit voltage from 708 mV to 718 mV and power conversion efficiency (PCE) from 19.3% to 20.1% was observed when the emitter of the cells was prepared at 170 degrees C-80 degrees C.