Polyimide substrate textured by copper-seeding technique for enhanced light absorption in flexible black silicon

This paper aims to present investigation on textured polyimide (PI) substrate for enhanced light absorption in flexible black silicon (bSi).

Flexible bSi with thickness of 60 µm is used in this work. To texture the PI substrate, copper-seeding technique is used. A copper (Cu) layer with a thickness of 100 nm is deposited on PI substrate by sputtering. The substrate is then annealed at 400°C in air ambient for different durations of 60, 90 and 120 min.

With 90 min of annealing, root mean square roughness as large as 130 nm, peak angle of 24° and angle distribution of up to 87° are obtained. With this texturing condition, the flexible bSi exhibits maximum potential short-circuit current density (J_max) of 40.33 mA/cm², or 0.45 mA/cm² higher compared to the flexible bSi on planar PI. The improvement is attributed to enhanced light scattering at the flexible bSi/textured PI interface. The findings from this work demonstrate that the optimization of the PI texturing via Cu-seeding process leads to an enhancement in the long wavelengths light absorption and potential J_max in the flexible bSi absorber.

Demonstrated enhanced light absorption and potential Jmax in flexible bSi on textured PI substrate (compared to planar PI substrate) by Cu-seeding with different annealing durations.