Confusion regarding the I-V characteristics of a solar cell
Not sure I can answer all of your question, but...

...we need to apply an 0.6v across the solar cell to make it work?

No. The circuit diagram that you embedded in your question really is a good model. The sunlight forces a constant current flow, and when current is forced through a diode in the forward direction, there must be a voltage &quot;drop&quot; (i.e., the 0.6V).  If the external circuit is able to accept that much current at a significantly lower voltage, then substantial current will flow through the external circuit, and not so much through the diode.
The edge cases would be a short circuit (virtually all of the current flows through the short, and the voltage is practically zero because of the low resistance), or an open circuit (All of the current flows through the diode because there is no other available path, and the terminal voltage is the full &quot;diode drop.&quot;)