Optimal design of thin film photoelectrochemical cell and thermoelectric hybrid systems

Abstract

A hybrid system in an integrated design is successfully fabricated, which consists of a silicon thin film photoelectrochemical cell (PEC) and a thermoelectric device (TE). The overpotential of c-Si substrates required for H2 evolution increases with the c-Si thickness decreasing because of a high surface recombination happened due to the surface minority carrier lifetime decreasing with decreasing the c-Si thickness. In the hybrid system, a PEC device as a photon-active element and a TE device as a phonon-active element separately generate a photovoltage and a thermovoltage, respectively. The thermovoltage acts as some compensation to the external voltage, consequently, reduces the overpotential. Owing to fully exploiting the solar spectrum, the system produces a sufficient voltage to drive the water splitting. The thin film with different thickness (from 100μm to 20μm) contrast tests are conducted. For 100μm thin film PEC-TE system, the ratio of the shifted voltage amount to the temperature gradient is comparable to the TE device Seeback coefficient, however, with decreasing the c-Si thickness, it is increased firstly and then decreased, and shows the maximum value in the 30μm thin film PEC-TE system, about 56% improvement compared to the 100μm thin film PEC-TE system.