Article High Fill Factors of Si Solar Cells Achieved by Using an Inv...

Article Fill factor in organic solar cells can exceed the Shockley-Q...

Article On the fill factor of solar cells

Article The fill factor of a solar cell from a mathematical point of view

Article Fill factor in organic solar cells,

Dear Uday

Additionally to the above answers, I think pinholes which may founded in the absorber layer may affect on the fill factor, and this can be observed from CV measurements and SEM.

The factors in solar cell affecting the fill factor are i) Temperature effects. higher voltage at low temperature and lose voltage in high temperatures. ii) The energy conversion efficiency increases by reducing the reflection of incident light.

As Ms S Jaziri has already explained that temprature of cell affects the fill factor at higher temperature a low voltage production and at low temprature the higher voltage.The conversion efficiency increases by reducing the refelection of incident light. You may also study the fill factor by designing a wavy solar cell design to increase the absorption of incident light wave.

Dear all for observation

Ideal factor decreases with increase in temperature mathematically according to the following practical relation LnI/V=q/(n_i K_B T)+LnI_° , and this use to find n_i (ideal factor) from the slope, this mean after less steps n_i=(1/0.025)*(1/slope), where 0.025 V=V_th (thermal voltage) , here T at room temperature, and we can rewrite the equation as n_i=(q/K_BT)*(1/slope), therefore the idea factor reciprocal proportional with the temperature. Also, this calculations from dark current, therefore the ideal factor represented property of diode.

With my best wishes 

Fill factor in solar cells is affected by resistive parameters in a such devices: front and rear metallic contacts resistivities, bulk ressitivity, n+ and p+ emmiters resistivities and metal-emitters interfaces resistivities. In your case, it is clear that the degradation is due to the bulk (active layer) resistivity. When increasing thickness of the active layer, you must characterize the structural and electrical properties of your thick layer. The rise of structural defects like micro-cracks lead to increasing of the series resitivity of the bulk which effect the FF of you solar cell.

In this case, you must adjust the deposit technological parameters of the active layer with a desirable thickness, to avoid the appearance (during deposit) of structural defects which act as active recombination centers leading to a low Jsc an Voc values and finally to a low FF values.

Hi Uday,

To add to all that has been said I will like to point out two things, assuming you are talking about organic solar cells (although these points may be valid for inorganic ones as well) and provided that pin holes are not issues here:

1. The observation that the FF (and therefore the PCE if all things equal) depends on the thickness is not new as the same is also observed for LEDs. It may be due to interference effect. It is well known that the efficiency of a PLED/OPV strongly depends on the active layer thickness. This is due to microcavity effects .

2. It could also be due to charge carriers mobility. The effect is well observed for example when you do degradation studies. It is observed that changes in the mobilities of the carriers affect greatly the FF as an end result. Thus, the real effect is on the rate of recombination and extraction rates in your system. This could mean that the varying thickness of your active layer affects the mobility of your carriers.

I hope you find this helpful.

A good starting point for understanding many of the contributing factors to the FF in organic bulk heterojunction solar cells is described nicely here:

Article Competition between recombination and extraction of free cha...

As a practical answer to your question, when you increase the thickness of the absorbing layer, you are increasing the light absorbed resulting to increase in charge carriers and increase in Jsc. Also, you are increasing Voc since more charge carriers will now be far away from the surface (which is a recombination site). However, if you continue increasing the thickness, the charge carriers are now also far away from the junction, which increases their potential for recombination. The parameter that you should take note if is the diffusion length of the charge carriers for your material at a certain doping and temperature.

Dear respected Uday Saha,

The factors of the solar cell that the its fill factor are

1. Output current at maximum power, Imp

2. Output voltage at maximum power , Vmp

3. Maximum output power, Pm

3. short circuit current, Isc

4. open circuit voltage, Voc

Best regards

Kifilideen

Fill factor mainly depend upon the morphology of the thin film.