Organic conjugate semiconductor, poly (3,4-ethylenedioxythiopene): poly (styrene sulfonate) (PEDOT:PSS) and silicon (Si) based hybrid heterojunction solar cells (HSCs) have shown tremendous potential as an alternative low-cost approach to the traditional crystalline Si (c-Si) solar cell technology. In the HSCs, opto-electronic properties of the organic layer play critical part in the junction formation and hence the performance of device. Therefore, the present study aims at tailoring the PEDOT:PSS thickness via spin speed variation of the organic solution and investigate its effect on morphological (PEDOT:PSS/Si interface), optical, surface passivation property and the device (HSCs) performance parameters. The results are further supported by comprehensive analysis of FESEM, UV–Vis–NIR, minority carrier lifetime, dark and illuminated J-V characteristics, quantum efficiency and electrochemical impedance spectroscopy (EIS) results of the solar cells utilizing the low-cost solar grade and thin Si wafers. The PEDOT:PSS layer exhibits anti-reflective and surface passivation properties in addition to forming efficient junction with n-Si. It has been found that the thickness of 140 ± 24 nm is the optimum for efficient HSCs on polished Si surfaces, with maximum efficiency of 8.89% contributed by the best optical, passivation and PEDOT:PSS/Si junction properties for effective generation of the charge carriers, separation and hence their transportation to the respective electrodes in the most fundamental device structure of ‘Ag/PEDOT:PSS/n-Si/In:Ga’. The present work may guide to the development of PEDOT:PSS/n-Si based optoelectronic devices via simple low thermal budget solution process.