Preventing page reload on submit

am trying to prevent this form from causing the whole page to refresh. When I've searched elsewhere on here, the answer is usually to use return false; However, this is already in the code but it's still reloading the page

<input type="submit" name="PC13871$btnRefresh" value="Search" onclick="(function(btn){var bDisableMe=true;if(typeof(Page_ClientValidate)=='function'){bDisableMe=Page_ClientValidate('PC13871');}__doPostBack('PC13871$btnRefresh','');btn.disabled=bDisableMe;})(this);return false;" id="PC13871_btnRefresh" class="BBFormSubmitButton DirectoryFormSubmitButton"></input>

Anyone got any ideas? This code is generated by a CMS so I can attack it with javascript/jQuery but can't just edit the html unfortunately.