We have custom-engineered dye-sensitized solar cells (DSCs) by eliminating spacers and holes, fabricating hole-free spacer-free (HF-SF) DSCs with 96% active area to total area ratio. These newly engineered HF-SF dye cells provide better scalability, lower cost, and improved aesthetics with enhanced device performance delivering more than 30% efficiency under indoor/ambient illumination. Two serially interconnected HF-SF DSCs fabricated using D35:XY1b co-sensitized organic dyes and [Cu (I/II)(dmp) 2] electrolyte were able to autonomously power an indoor temperature and humidity monitoring unit free of batteries at realistic indoor illumination intensities below 200 lux.