You can try this.It works i think so
$form['formItem'] = array( '#type'=>'text_format', '#title' => t('Field Label'), '#value' => 'This is my value', '#format'=>'full_html', );
$form['formItem'] = array(
'#type'=>'text_format',
'#title' => t('Field Label'),
'#value' => 'This is my value',
'#format'=>'full_html',
);