kartik gridview export pdf font size

Hi, i am using kartik gridview. I use the gridview export to export content to pdf, but the problem is the generated pdf font is too small. I has try set defaultFontSize as below, no error, but does not work. orientation also not working, but can be replace with ‘format’ => ‘A4-P’.

'exportConfig' => [

        'pdf' => [            

            'config' => [

                'defaultFontSize' => 24,

                'orientation' => 'P',

                // 'format' => 'A4-P',




So the remain problem is how to change font size?