In his first ever investment overseas, Wipro's billionaire chairman Azim Premji has invested around $15 million in Vinod Khosla's clean-tech fund in the US, the biggest such fund focused on returns from Silicon Valley's hottest start-ups.

With nearly $1.5 billion corpus, Premji Invest, the investment arm that manages the Wipro founder's wealth, now plans to look beyond India for diversifying its portfolio and also tap into lucrative opportunities offered by new technology companies in the US.