We report on flexible photovoltaic cell fabricated on polymeric substrate optimized for indoor energy harvesting. We have fabricated small area modules (up to 30 cm2) obtained by monolithic integration of a-Si:H p-i-n solar cells deposited by PECVD at low temperature with excellent mechanical strength, high ability of folding and very good stability. The photovoltaic thin film module is optimized for indoor light generated by indoor lamps and has efficiency as high as 9.1% on aperture area even at less than 100 lx of light intensity (under F12 fluorescent lamp spectrum). The optimized system can be used to energize thin film batteries and can be assembled in a flexible system associated with a wireless sensor network or other electronic devices.