Development of Thin Film Amorphous Silicon Tandem Junction Based Photocathodes Providing High Open-Circuit Voltages for Hydrogen Production

Hydrogenated amorphous silicon thin film tandem solar cells (a-Si: H/a-Si: H) have been developed with focus on high open-circuit voltages for the direct application as photocathodes in photoelectrochemical water splitting devices. By temperature variation during deposition of the intrinsic a-Si: H absorber layers the band gap energy of a-Si: H absorber layers, correlating with the hydrogen content of the material, can be adjusted and combined in a way that a-Si: H/a-Si: H tandem solar cells provide open-circuit voltages up to 1.87V. The applicability of the tandem solar cells as photocathodes was investigated in a photoelectrochemical cell (PEC) measurement set-up. With platinum as a catalyst, the a-Si: H/a-Si: H based photocathodes exhibit a high photocurrent onset potential of 1.76V versus the reversible hydrogen electrode (RHE) and a photocurrent of 5.3mA/cm(2) at 0V versus RHE (under halogen lamp illumination). Our results provide evidence that a direct application of thin film silicon based photocathodes fulfills the main thermodynamic requirements to generate hydrogen. Furthermore, the presented approach may provide an efficient and low-cost route to solar hydrogen production.