Hii ..

For the admission in IISER through SCB , candidates have to score  within cutoff.

For admission in IISER through SCB a candidate must have to :-

•  Candidate have to pass 10+2 with science stream .

• For admission candidates have to score within in cut-off .

• Candidates whi apply should appear for IAT exam.

IISER have different percentage Cut-off for different board of India :-

Board .           % cut-off

Kerala.             93.3 

CBSE.                90          

Assam.              74 .5

Chhattisgarh .      76.6

Maharashtra .       77.9

Now As you have 81% and you belong to Kerala .. sorry  to say  .but you no able to apply for IISER ..but you can definitely try for other...

All the best !!