Ultrathin Si solar cell with nanostructured light trapping by metal assisted etching

We report an 8 µm-thick silicon solar cell with an efficiency of 9.60%. Nanostructured silicon surface formed via metal assisted etching shows a broadband reflection below 10%. Despite the excellent optical performance, a moderate short-circuit current (JSC) of 25.44 mA/cm2 was collected. Relatively low external quantum efficiency (EQE) at short wavelengths was associated with carrier recombination at the enhanced surface and by the Auger process. Moreover, parasitic absorption at the back contact is the main factor resulting a relatively low EQE in long wavelength region of the spectrum. Our optical simulations show that planarization of the rear Si surface and insertion of a low refractive index dielectric spacer between Si and the rear metal can significantly reduce the parasitic absorption in the metal, resulting in JSC values over 35 mA/cm2.