In this proposal, we present a novel design approach based ontwo-dimensional (2D) van der Waals (vdW) heterostructures. These 2D materials possesspeculiar properties, including mechanical flexibility, tunable bandgaps, strong light-matterinteraction, and stackability with no limitation of lattice matching. These make vdWheterostructures promising to build devices that are flexible and light as well as efficient andstable. Scientific Objective: Designing and Synthesizing Ruddlesden-Popper perovskites (RPP)and Indium selenide (InSe) single crystals. Stacking of new vdW-heterostructures of RPP/InSewith defined interface engineering for an improved charge separation. Fabrication of flexibleand rigid photodetector and solar cell devices. Detailed investigation under both mechanicalstrain and light to assess stability, efficiency and flexibility. Hypothesis: In this work, wehypothesis that well-designed vdW heterostructures-featuring optimal band alignment, stronginterlayer coupling, and reduced defect at the interface will allow for a high-performanceoptoelectronic device that possesses both excellent charge transport and mechanicalproperties. Thinning the absorber layer and tuning the heterointerfaces are likely the twomain design parameters to improve the performance and the flexibility simultaneously.Impact: The successful execution of this project could make important contribution to thedevelopment of flexible and low-cost optoelectronics. It should lead to profound understandingfor the interlayer interaction, charge transport kinetics, and the device stability of 2D devices.Most importantly, this work offers an engineering avenue for high-performance vdW materialsin wearable electronics, and portable energy harvester and the next-generation sensingapplications.