The generation of sustainable electrical energy from wasted environmental mechanical stimuli is a necessary step for supplying low-power devices in this digitalization era. Sustainable polymers are an attractive class of materials for energy harvesting applications due to their abundance, low ecological impact, and simple and low-cost processing for polymer-based devices. Thus, solvent-processed hydroxypropyl cellulose (HPC), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly-l-lactic acid, and silk fibroin were evaluated as active materials in triboelectric nanogenerators with the aim of replacing non-sustainable synthetic materials. Harvesting devices incorporating sustainable polymers demonstrate superior performance compared to some established materials in the triboelectric series. Notably, HPC and PHBV outperform aluminum, emerging as novel, flexible, and solvent processable sustainable materials that can be included in the triboelectric series as positive tribomaterials. Furthermore, when combined with piezoelectric polyvinylidene fluoride (PVDF), these polymers exhibit enhanced performance as hybrid piezoelectric–triboelectric nanogenerators. The output voltage of the HPC–PVDF pair reaches voltages up to 100 V. This combination demonstrates the feasibility of using sustainable materials to achieve improved energy-harvesting capabilities while supporting eco-friendly devices with a variety of designs based on solvent based processability, compatible with additive manufacturing.