Fig. 4. (a) Variation of maximum STH efficiency (%) with redox mediator potential (V vs. SHE) plot for the side by side (green) and tandem configuration alternatively with HEP (red) or OEP (blue) on top. The dashed and solid lines indicate the ideal case (no overpotentials) and non-ideal case (with overpotentials), respectively. (b) STH efficiency (%) as a function of the HEP's (x-axis) and OEP's (y-axis) bandgap energy in ideal top-bottom configuration (in terms of optical arrangement) with HEP on top at redox mediator potential of 1.0 V vs. SHE.