<p>Replacing expensive platinum with low-cost and sustainable materials is important for large-scale dye-sensitized solar cell (DSSC) production. In this study, bean curd stick residue, a protein-rich industrial biowaste, was utilized as an innovative precursor for synthesizing heteroatom-doped porous carbon counter electrodes. Porous carbon materials were prepared from bean curd stick residue and doped with boron, phosphorus, and sulfur to enhance their electrochemical properties. This approach combines sustainable waste utilization with systematic heteroatom modification to achieve improved catalytic and photovoltaic performance in DSSCs. XRD results confirmed the amorphous nature of the carbon. FTIR and Raman results verified successful heteroatom doping. Morphological studies showed a uniform and highly porous structure. BET analysis revealed that the sulfur-doped carbon had the highest surface area of 322 m²&#xa0;g⁻¹. Among all samples, sulfur-doped carbon showed the best performance with a power conversion efficiency of 7.40%, which was very close to that of the platinum-based cell (7.60%). Electrochemical tests (CV, Tafel, and EIS) indicated fast charge transfer and low resistance for sulfur doped carbon. The device retained over 96% of its initial efficiency after 30&#xa0;days, demonstrating stable long-term performance. Beyond a descriptive comparison, we establish a structure–property–performance relationship linking dopant-induced defect density (Raman I_D/I_G) and electrochemically active surface area (Cdl) to interfacial charge-transfer resistance (Rct), exchange current density (J₀), and device PCE, thereby rationalizing the superior performance of S–BCS via its C–S/C = S active sites and enhanced interfacial kinetics. Overall, this study highlights a green and scalable strategy for fabricating high-performance, heteroatom-doped carbon electrodes from bean curd stick waste, offering a sustainable route toward next-generation Pt-free DSSC technology.</p>