SHANGHAI • The controversial boss of Chinese solar energy firm Hanergy Thin Film Power Group - once listed as China's richest man - has stepped down as chairman and executive director, the company said, almost a year after its shares imploded.

Mr Li Hejun stepped down on Friday "for the reason of strengthening corporate governance", Hanergy said in a statement to the Hong Kong Stock Exchange, where its shares have been suspended since May last year after plunging 47 per cent in less than half an hour, wiping US$19 billion (S$26 billion) off its market capitalisation.

Hong Kong's securities regulators also announced a probe into the company.

Hanergy had captured the attention of investors after growing more than sixfold to became the world's largest solar power company by market value before the collapse, amid questions over the firm's share price and revenue sources.

The meteoric rise in share price once gave Mr Li the title of China's richest man, according to one wealth survey.

However, he has since fallen well down the rankings and regulatory filings showed he later sold some of his shares at a 95 per cent discount.

Mr Li, founder of Hanergy Holding, controls more than two- thirds of the stock of the listed subsidiary and remains chairman and chief executive officer of the parent company, which has been investing in thin-film solar technology since 2009.

"I don't think that will make much difference" to the regulators or stop the investigation, shareholder activist David Webb said by phone.

Hong Kong's Securities and Futures Commission did not reply to an e-mail seeking comment.

Hanergy's statement said there were no matters relating to Mr Li's resignation that needed to be brought to the attention of the stock exchange or shareholders.

The Securities and Futures Commission has yet to make a public announcement about its investigation, almost a year after it started.

Two other executive directors of Hanergy Thin Film also stepped down, according to the latest statement, with Mr Yuan Yabin, a deputy general director of the parent company, taking over as chairman and an executive director of the listed unit.

The collapse of Hanergy and some other top-performing stocks on the Hong Kong stock market prompted critics to question the oversight of regulators.

AGENCE FRANCE-PRESSE, BLOOMBERG