Solution-Processed Black-Si/Cu₂ZnSnS₄ Nanocrystal Heterojunctions for Self-Powered Broadband Photodetectors and Photovoltaic Devices

We report, for the first time, the fabrication of n-black Si (B–Si)/p-Cu2ZnSnS4 nanocrystal (CZTS NC) heterojunctions to demonstrate their photodetection and photovoltaic characteristics. Inks with crystalline CZTS NCs can be directly spin coated on an ultralow reflective (<1.5% in the visible range) metal-assisted chemical-etched black Si to fabricate solution-processed B–Si/CZTS heterojunctions, with the process compatible for large area applications. Fabricated devices operate as self-powered visible to near infrared (vis–NIR) wideband photodetectors, with a high Iph/Idark ratio of ∼105, a very fast switching speed (∼μs), and remarkably high figure-of-merits at zero bias. Furthermore, an optimal thickness of NC layers exhibits superior photovoltaic characteristics with an efficiency >5.0%, even without any surface passivation or encapsulation of the device. The combined studies show impactful potential of the B–Si/CZTS NC heterojunction for future high-speed light-sensing and energy-harvesting devices using solution-processed techniques compatible to large area applications.