III-V semiconductors are favoured photo absorber materials for solar energy conversion due to their ideal bandgap, yet their high-cost hinders widespread adoption. Utilizing thin films of these semiconductors presents a viable way to address the cost-related challenges. Here, a novel mechanical exfoliation technique is demonstrated, also known as controlled spalling, as a cost-effective and facile way to obtain thin films of III-V semiconductors. As a proof of concept, 15 μm thick InP films are successfully exfoliated from their original wafers. Thorough characterization using cathodoluminescence and photoluminescence spectroscopy confirms that the opto-electronic properties of the exfoliated InP films remain unaffected. Utilizing these InP thin films, InP thin-film heterojunction solar cells with efficiencies exceeding 13% are demonstrated. Additionally, InP photoanodes are fabricated by integrating NiFeOOH catalyst onto these InP thin-film solar cells, achieving an impressive photocurrent density of 19.3 mA cm-2 at 1.23 V versus reversible hydrogen electrode, along with an applied bias photon-to-current efficiency of ≈4%. Overall, this study showcases the efficacy of controlled spalling in advancing economically viable and efficient III-V semiconductor-based solar energy conversion devices.