You are designing a silicon photovoltaic cell to operate at 300 K. The target wavelength is 650 nm, for which silicon has an absorption coefficient of 5000 cm-1. Both the p- and n-type regions have dopings of 4 1015 cm-3, and the metallurgical junction is located 0.5 m below the surface (with the p-type semiconductor at the surface). The pn junction has a cross-sectional area of 0.4 cm2.

a) Between what depths from the surface does the space charge region exist?

b) Neglecting reflections at the surface, what percentage of the incoming light is absorbed in the space charge region?

c) To capture more light, a fully depleted/compensated intrinsic (i) region can be placed between the p- and n-type regions. How large would the i-region need to be if 75% of the incoming light is required to be absorbed?

d) For the p-i-n structure, what is the total short-circuit current generated (ISC) if the excess carrier lifetime is 9.5 10-7 s, and there are 1.1 1010 cm-2s-1 photons hitting the surface of the device. Again, neglect reflections at the surface.

e) A measurement of the current shows that you captured more carriers than the calculation performed. Describe a process to support the measurement (other than reflections).

f) What is the maximum ideal power that the device could generate? Compare this to the total optical power available.