Dear Ahmed,

Several terms have been adopted to describe the efficiency for converting solar energy, namely the Applied Bias Photon-to-Current Efficiency (ABPE), and Quantum Efficiency (QE). ABPE is usually used to characterize the photo-response efficiency of a photoelectrode material under an applied voltage.

ABPE sometimes is referred to as the photo-conversion efficiency. Due to the voltage applied, such terms cannot be used to represent the true photo-conversion efficiency for photocatalytic water splitting.

The definition of photo-conversion efficiency is shown in Equation:

nABPE (%)= [(Total power output - electrical power input)/(light power input)] *100%

where E0(rev) is 1.23 V, the standard state-reversible potential, I0 is the power density of incident light, and Eapp is the applied potential.

As for quantum efficiency, it can represent the characteristic photon conversion of photoactive films. It is defined as the percentage of generated electrons and incident photons while the photoactive films

are irradiated under a specific wavelength, as shown in Equation:

nQE =Neff/Ntot

In the above equation, Neff is the number of effective generated electron-hole pairs under light irradiation, and Ntotal is the total number of incident photons. It is noted that ηQE neglects the energy loss of solar irradiance and the chemical conversion efficiency. Therefore, it is suitable to qualify the photoactive films but not to represent the water-splitting reaction conversion efficiency.

To describe the true hydrogen production efficiency of a water-splitting reaction under sunlight, a term called “solar-to-hydrogen” conversion efficiency (STH)  is often used. The definition of STH conversion efficiency is shown in Equation:

STH=(Jscx1.23xnF)/Ptot

where, Ptotal represents the power density of incident simulative sunlight (AM1.5G) and the numerator is the product of photocurrent density (jsc) at zero bias (short-circuit photocurrent), the thermodynamic voltage required for water splitting (1.23 V), and the faradic efficiency (ηF).

Dear Prof. Dr. Maria Vasilopoulou 

Thank you so much for your generous answer. Actually  I used the applied Bias photoconversion efficiency  equation to calculate the efficiency  of TiO2 nanotube arrays where I subtracted the known value of the applied external potential.. In this case how far we can consider the calculated efficiency accurate ?

another question, if I add 0.5 vol. % Ethylene glycol to the electrochemical 1 M KOH aquous solution (as a hole scavenger), is the above  mentioned equation still accurate and could be used to calculate the photoconversion efficiency ?

Thank you

U can also use IPCE which is incident photon to current conversion efficiency. 

Thanks to Dr. Maria Vasilopoulou  for her perfect answer. I think that adding EG doesn't change any thing. You can use those formulas as well.

The area of fotocathode increase the efficiency ? looking to 3C-SiC ethero growth on 6 inch wafer ?

Ahmed El Ruby Mohamed you want to add 0.5 vol. % Ethylene glycol in 1 M KOH solution as a hole scavenger to calculate the photoconversion efficiency, you cannot use sacrificial donor or acceptor in the electrolyte for ABPE measurement because it will fail to represent a stand-alone water splitting process, it may useful in analyzing interfacial charge transfer limitations.

Ahmed El Ruby Mohamed

If you have LSV data of your material you can find out the applied bias photon-to current conversion efficiency. You can find the formula/equation of ABPE in several research articles in the field of photo-electrochemical water splitting. I hope this answer will help you. Best luck with your research !!