This article presents ultrathin and lightweight organic solar cells with high flexibility, fabricated on 1.4-μm-thick polyethylene terephthalate (PET) substrates. These solar cells achieve a power conversion efficiency of 4.2% and have an unprecedented solar cell-specific weight of 10 W/g. They are highly flexible and can withstand extreme mechanical deformation, including tensile strains of over 300%. The devices are constructed using standard processing methods, making them suitable for integration into other flexible electronics like light emitting diodes, capacitors, and transistors. The solar cells consist of a light-harvesting active layer, two electrodes, and blocking or transport layers. The total thickness of the device is less than a typical thread of spider silk, with the active layer accounting for about one-quarter of the total thickness. The solar cells are fabricated on a pre-stretched elastomer, allowing for reversible stretching and compression. The devices demonstrate excellent mechanical resilience, with performance metrics comparable to those on glass substrates. The solar cells were tested under various mechanical deformations, including uniaxial and biaxial compression, and showed stable performance even after multiple cycles. The devices can withstand up to 50% biaxial compression and re-stretching, with minimal loss in performance. The results indicate that ultrathin organic solar cells can be a viable solution for applications requiring lightweight, flexible, and durable power sources, such as electronic textiles, synthetic skin, and robotics. The study highlights the potential of ultrathin organic solar cells for future applications due to their high flexibility, low weight, and mechanical resilience. The devices are fabricated using standard methods, making them suitable for large-scale production. The research also addresses the challenges of using organic photovoltaic (OPV) cells, including the need for cost-effective and scalable manufacturing processes. The results demonstrate that ultrathin OPV cells can achieve performance metrics comparable to those of conventional solar cells, making them a promising technology for future flexible and lightweight power sources.This article presents ultrathin and lightweight organic solar cells with high flexibility, fabricated on 1.4-μm-thick polyethylene terephthalate (PET) substrates. These solar cells achieve a power conversion efficiency of 4.2% and have an unprecedented solar cell-specific weight of 10 W/g. They are highly flexible and can withstand extreme mechanical deformation, including tensile strains of over 300%. The devices are constructed using standard processing methods, making them suitable for integration into other flexible electronics like light emitting diodes, capacitors, and transistors. The solar cells consist of a light-harvesting active layer, two electrodes, and blocking or transport layers. The total thickness of the device is less than a typical thread of spider silk, with the active layer accounting for about one-quarter of the total thickness. The solar cells are fabricated on a pre-stretched elastomer, allowing for reversible stretching and compression. The devices demonstrate excellent mechanical resilience, with performance metrics comparable to those on glass substrates. The solar cells were tested under various mechanical deformations, including uniaxial and biaxial compression, and showed stable performance even after multiple cycles. The devices can withstand up to 50% biaxial compression and re-stretching, with minimal loss in performance. The results indicate that ultrathin organic solar cells can be a viable solution for applications requiring lightweight, flexible, and durable power sources, such as electronic textiles, synthetic skin, and robotics. The study highlights the potential of ultrathin organic solar cells for future applications due to their high flexibility, low weight, and mechanical resilience. The devices are fabricated using standard methods, making them suitable for large-scale production. The research also addresses the challenges of using organic photovoltaic (OPV) cells, including the need for cost-effective and scalable manufacturing processes. The results demonstrate that ultrathin OPV cells can achieve performance metrics comparable to those of conventional solar cells, making them a promising technology for future flexible and lightweight power sources.