Question

why can not we use DC current instead of using AC current after it reaches our home appliances using diode

Answer 1

In our homes we use AC because you can change the value of the voltage very easy with transformers. Its very important to step up the voltage (and step down the current, so power remains the same) generated from the power station and transmit it at this stepped up voltage to minimize losses. Then we have to step down the voltage down to safe levels to be able to use it with safety (this doesnt mean that it cant still kill you) at home. As i said this is achieved easily with transformers. With DC is more complicated and expensive to make this conversion in voltage levels thus we use AC.