There could be more than one reason:

1) It could be due to the perovskite layer. Did you check the perovskite film (not the ones you made devices on) using SEM (for film morphology) and XRD (cor crystal structure).

2) Spiro-OMeTAD can also be the reason. How did you process spiro-OMeTAD?

How does the J-V curve look like (shape) by the way?

Sanjib Das, Thanks for your comments.

I am following the same procedure as reported in http://www.nature.com/nnano/journal/v9/n11/full/nnano.2014.181.html

The morphology and XRD data are similar to the reported one.

What should we do for Spiro-OMeTAD, I mean concentration and spinner spead?

J-V curve little bend from line, the FF is in the range of 28-35%.

Kindly suggest me what I should do.

Dear Firoz,

You have two problems with your solar cells:

The the problem of small short circuit current, and

- relatively small fill factor.

From the basic point of view, the short circuit current is reduced because of the exceive recombination of the generated excitons in the active perovskite layer and the recombination of the electron hole pairs at the interfaces of the active layer with the HTL and the ETL.

The cause of this excessive recombination is the too long thickness of the active layer such that the excitons  have to diffuse longer distance than their diffusion length. 

The higher recombination at the interface with the transport layer because of the of the energy level misalignment at the interfaces and the smaller mobility of the holes and electrons in the transport layer.

If the energy levels at the interfaces are mismatched the interface acts as a rectifying contact with high resistance leading to the appearance of the  S-shaped 

illuminated IV curve. This reduces both the short circuit current and the fill factor.

So. one has to give the interfaces to the active material the highest priority. 

So, if the materials are standard, you have to take care of the layer thicknesses and the surfaces before the deposition and the deposition condition. You have to systematically avoid any contamination. 

wish you success