High flexibility and industrial compatibility are the key factors for developing large-scale lightweight, wearable, and portable thin film flexible solar cells. The three-dimensional (3D) silicon p-i-n radial junction (RJ) structure, grown via a low-melting-point metal-catalyzed VLS process in a plasma-enhanced chemical vapor deposition system, provides an ideal framework for fabricating radially stacked thin film solar cells, which possesses a strong light trapping effect and large built-in field, facilitate carrier collection, suppress light-induced-degradation (LID) effect. Though flexible RJ cells have been successfully demonstrated in our group, taking 15 μm thick Al foil as substrate, the soft Al foils alone, with relatively low mechanical strength and stability, is still not a strong enough substrate for sustain large number repetitive bending or subject to lasting stretching strain.
Here, a rather flexible and mechanically durable 3D RJ solar cell has been directly constructed upon flexible ZnO-coated stainless steel (SS) foil substrates. The ZnO layer deposited on the SS surface can optimize the density of SiNWs to improve the optoelectronic performance. A power conversion efficiency of 6.01% has been accomplished, with open-circuit voltage and photo-current density of 0.76 V and 12.87 mA/cm², respectively. Remarkably, the outstanding mechanical stability of these RJ devices has been recorded, which can sustain >4000 cycles of large bending to a radius of 2.5 mm, with only a 7% efficiency decrease. Note that the one-pump-down fabrication procedure of this 3D nanostructure RJ cells upon flexible ZnO-coated SS substrates is compatible with the industrial-mainstream Roll-to-Roll technology, holding thus a strong promise to establishing a simple and low-cost strategy for high-performance and durable flexible photovoltaics.