Why the optical gap is not identical to the charge gap? The optical gap is the photon energy required to create an exciton (in a solar cell for example). The charge gap (aka electrical gap) is the energy (voltage) required to create a photon (in an LED for example). Why are these two gaps not identical?
Ref:

Undoped (neutral) conjugated polymers are semiconductors, with optical
  gaps of ~ 2-3 eV and charge (or band) gaps typically ~ 0.5-1.0 eV
  higher in energy, reflecting the large exciton binding energies in
  polymers. (source: Barford, 2013)

(source)
See also: What is the basic difference between optical band gap and electrical band gap?
 A: The difference between the fundamental gap (following IUPAC definitions - and your diagram ) (this is what you refer to as your electronic gap in your question) exists because the optical gap corresponds to the energy of the lowest electronic transition accessible via absorption of a single photon. The optical gap is generally substantially lower than the fundamental gap. 
The reason for this is that that in the excited state the electron and the hole remain electrostatically bound to one another. This means the magnitude difference between the fundamental gap and the optical gap is related to the binding energy. 
The fundamental gap corresponds to the different energy caused due to the sharp bound between eigenvalues in the Schrodinger operator.
So in the diagram you have provided, the fundamental gap is labelled $E_{fund}$, the electron-hole pair binding energy $E_{B}$ is given by $E_{fund}-E_{opt}$. 
Non Technical Summary
The optical gap only lists an electron over the band gap and you must account for the electrostatic effects between your hole and the electron. 
The fundamental/electronic gap is the proper quantum energy difference between the energy levels.. 
A: The optical or vertical bandgap is the minimum separation between the valence and the conduction band at constant k-value, or electron momentum. The charge bandgap is the separation of the  conduction and valence states where these may have different k-values. The optical bandgap is always larger than the charge band gap. Exciton states have an energy somewhat smaller than the optical band gap. The difference is the binding energy, a fraction of the optical band gap. 
