Some embodiments of the present disclosure relate to a deep trench isolation (DTI) structure configured to enhance efficiency and performance of a photovoltaic device. The photovoltaic device comprises a functional layer disposed over an upper surface of a semiconductor substrate, and a pair of pixels formed within the semiconductor substrate, which are separated by the DTI structure. The DTI structure is arranged within a deep trench. Sidewalls of the deep trench are partially covered with a protective sleeve formed along the functional layer prior to etching the deep trench. The protective sleeve prevents etching of the functional layer while etching the deep trench, which prevents contaminants from penetrating the pair of pixels. The protective sleeve also narrows the width of the DTI structure, which increases pixel area and subsequently the efficiency and performance of the photovoltaic device.