This study demonstrates single-layer graphene/n-Si Schottky junction solar cells with a power conversion efficiency (PCE) of 8.6% under AM1.5 illumination, achieved by chemical doping with bis(trifluoromethanesulfonyl)amide (TFSA). This performance is 4.5 times higher than the native (undoped) device and nearly 6 times higher than the best previously reported PCE for similar devices. The enhancement is attributed to doping-induced shifts in the graphene chemical potential, which increase the graphene carrier density (reducing series resistance) and the cell's built-in potential (increasing open-circuit voltage), both of which improve the solar cell fill factor. The TFSA dopant offers environmental stability due to its hydrophobic nature. The improvements in PCE are explained through current-voltage, capacitance-voltage, and external quantum efficiency measurements. The increase in Schottky barrier height (SBH) and built-in potential (Vbi) as measured by J-V and C-V techniques, along with reduced resistive losses due to increased electrical conductivity of doped graphene, contribute to the enhanced performance. The study also addresses the physics governing electrical transport across the graphene/n-Si interface. The TFSA doping increases the SBH and Vbi, leading to more efficient electron-hole pair separation and collection. The PCE increases from 1.9% to 8.6% due to these factors. The environmental stability of the solar cells is attributed to the hydrophobic nature of TFSA, which preserves graphene's optical properties. The methods used are practical, simple, and scalable, involving conventional graphene production techniques and uncomplicated spin-casting of organic layers. The results show that chemical doping with TFSA significantly improves the performance of graphene/n-Si Schottky junction solar cells, making them more efficient than ITO-based devices. The study highlights the potential of graphene-based solar cells for future photovoltaic applications.This study demonstrates single-layer graphene/n-Si Schottky junction solar cells with a power conversion efficiency (PCE) of 8.6% under AM1.5 illumination, achieved by chemical doping with bis(trifluoromethanesulfonyl)amide (TFSA). This performance is 4.5 times higher than the native (undoped) device and nearly 6 times higher than the best previously reported PCE for similar devices. The enhancement is attributed to doping-induced shifts in the graphene chemical potential, which increase the graphene carrier density (reducing series resistance) and the cell's built-in potential (increasing open-circuit voltage), both of which improve the solar cell fill factor. The TFSA dopant offers environmental stability due to its hydrophobic nature. The improvements in PCE are explained through current-voltage, capacitance-voltage, and external quantum efficiency measurements. The increase in Schottky barrier height (SBH) and built-in potential (Vbi) as measured by J-V and C-V techniques, along with reduced resistive losses due to increased electrical conductivity of doped graphene, contribute to the enhanced performance. The study also addresses the physics governing electrical transport across the graphene/n-Si interface. The TFSA doping increases the SBH and Vbi, leading to more efficient electron-hole pair separation and collection. The PCE increases from 1.9% to 8.6% due to these factors. The environmental stability of the solar cells is attributed to the hydrophobic nature of TFSA, which preserves graphene's optical properties. The methods used are practical, simple, and scalable, involving conventional graphene production techniques and uncomplicated spin-casting of organic layers. The results show that chemical doping with TFSA significantly improves the performance of graphene/n-Si Schottky junction solar cells, making them more efficient than ITO-based devices. The study highlights the potential of graphene-based solar cells for future photovoltaic applications.