There is a review article which will give you an idea on the subject. You will also get some cross references from there which might help you.

Concept of any solar cell:

For any solar cell operation you require following:

1. A material which can absorb light in order to generate electron hole pair, more precisely charge carriers. Variety of semiconductors are known to full fill this condition and silicon is one of those material.

2. Spacial separation of generated electrons and holes before their recombination.

3. Collection of different type of photogenerated charge carriers (generated because of absorption of photon) at different contact in order to give net current in the circuit if two terminals are connected via load resistance.

When pn junction is formed from crystalline silicon, an electric field and depletion region is developed near the metallurgical junction. When you incident a photon of energy greater than band gap energy it will generate electron hole pair in the device. If generated electron hole pair are in depletion region they will be separated from each other in space because of electric field in depletion region. Because of electric field electron then goes to n type material and hole goes to p type material and eventually they will be collected at the respective contact. You can see direction of flow of charge in this case is opposite to what was supposed in the forward bias pn junction. So you can say your current is negative and you are getting -ve current out of the device without any biasing potential.

Now if you will forward bias the pn junction then your current will start decreasing (in magnitude) and it will be zero at some applied bias. That bias is known as open circuit potential of the cell and the current at no bias known as short circuit current of the cell. At any point between short circuit condition and open circuit potential if you will calculate the electric power you will get -ve value (+ve potential and -ve current) which says that you are not dissipating electric power in the device while you are getting some power out of it.

What if generation is not in the depletion region? Now that is very simple. If generation is within the diffusion length from the edge of depletion region those carriers are likely to go to the depletion region and contribute to photocurrent. While if the generation is away from diffusion length those carriers are likely to recombine before they reach the depletion region and doesn't contribute to photocurrent.

This was the basic concept of solar cell. If you want to know more detail you can go through the website:

http://www.pveducation.org/pvcdrom

In a conventional solar cell, light is absorbed by a semiconductor producing an electron-hole (e-h) pair; the electron hole pair may be bound and is referred to as an exciton. This pair is separated by an internal electric field (present in p-n junctions or Schottcky diodes) and the resulting flow of electrons and holes creates electric current. The internal electric field is created by doping one part of semiconductor interface with atoms which act as electron donors (n-type doping) and another with electron acceptors (p-type doping) that results in a p-n- junction. Generation of an e-h pair requires that the photons of light have energy exceeding the band gap of the material.

Effectively, photons with lower energies than the bandgap do not get absorbed (depends on whether the semiconductor is direct or indirect, and the exact absorption coefficients), while higher energy photons are relatively inefficient as an energetic e-h pair can quickly (within about 10−13 s) thermalize to the band edges, thus reducing the energy of the extracted carriers. The former limitation results in a lower current scenario, while the thermalization reduces the maximum achievable cell voltage. As a result, all semiconductor solar cells suffer a trade-off between voltage and current (which can be in part alleviated by using multiple junction implementations).

Efficiency of a solar is defined as the ratio of energy output from the solar cell to input energy from the sun. In addition to reflecting the performance of the solar cell itself, the efficiency depends on the spectrum and intensity of the incident sunlight and the temperature of the solar cell. Therefore, conditions under which efficiency is measured must be carefully controlled in order to compare the performance of one device to another. Terrestrial solar cells are measured under AM1.5 conditions and at a temperature of 25°C. Solar cells intended for space use are measured under AM0 conditions.

The efficiency of a solar cell is determined as the fraction of incident power which is converted to electricity and is defined as:

Pmax= Voc. Isc.FF.

Eta (Coefficient of efficiency) = Voc. Isc.FF/Pin.

Voc (open cicuit voltage), Isc (short circuit current, Pin (Input power; generally at 10W) and FF9 (Fill Factor=0.83-0.85 for Si solar cell).

FF= Voc-ln (Voc+0.72)/Voc+1.

Numerical analysis shows that the 31% efficiency is achieved when the solar cell material has a bandgap of 1.3-1.4 eV, corresponding to light in the near infrared. THIS BAND GAP IS CLOSE TI THAT OF SILICIN(1.1 eV); ONE OF THE MANY REASONSTHAT THIS MATERIAL DOMINATESSOLAR CELL PRODUCTION . However, silicon's maximum efficiency is maximized at about 29%. It is possible to greatly improve on a single-junction cell by stacking cells with different bandgaps on top of each other – termed the "tandem cell" or "multi-junction" approach. The same basic analysis shows that a two layer cell should have one layer tuned to 1.64 eV and the other at 0.94 eV, with a theoretical performance of 44%. A three-layer cell should be tuned to 1.83, 1.16 and 0.71 eV, with an efficiency of 48%. An "infinity-layer" cell would have a theoretical efficiency of 86%, with other thermodynamic loss mechanisms accounting for the rest.