Let's be honest here. If you have a solar panel powered mobile phone, you will have to sit under the sun or keep your phone under the sun for around 3 to 4 hours to charge it. Do anyone have time to do that ? And even if you have time, will you sit under the sun along with your phone if you have to use it while charging ?
Solar technology has numerous applications that seem to be very cool and innovative. But at the end, what matters is its usability.
But yes, if you are from the rural part of the country, having a solar mobile phone charger or solar powered mobile battery is a good option.
I would consider solar power mobile battery charger as a luxury product that I can use while I'm travelling to mountains or to villages or going for a long trek. But for a regular use, nah !!