You must be sure that you modeled correctly the led and the photo diode separately. Then you let the LED illuminate the photo diode. The LED model is a diode emitting light flux with certain intensity and wavelength. The model of the photo-diode is a controlled current source proportional to the incident light intensity. The conversion efficiency  of the diode depends on the light wavelength. You have to reverse bias the diode and add a resistance in series with it to sense the current passing through the diode. You can access the voltage across the resistance , it will indicate the strangeness of the light falling on the diode.If you give information about your model, you may get more support to trouble shoot your system.

wish you success

Dear Researcher

please refer to this attachments.it would be helpful for you.

Regards

http://www.arpnjournals.com/jeas/research_papers/rp_2015/jeas_0415_1849.pdf

http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=7342278&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D7342278

you can check this also.

http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=7342278&url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel7%2F7332129%2F7342249%2F07342278.pdf%3Farnumber%3D7342278

http://www.sciencedirect.com/science/article/pii/S0030401815000139

How to connect this photodiode to scope in simulink? (in fig)

The circuit as in fig has an error. Please change the position of the photodiode and the resistor such that the the resistor is connected between the anode of the diode and the ground which is connected to the power supply. Then connect two wires to the oscilloscope across the resistor, The positive is at the node of the diode and the resistor and the negative is at the ground point.

In this way your circuit oscilloscope will show the voltage on the resistor = I xR. Knowing R you can calculate the diode current I.

wish you success