If your device has broken power key, you can use Volume Unlock to instead it. Volume Unlock will help you wake lock screen so you can interact with screen.

[Featured]
✔ Support widget to screen off
✔ Support Screen Off from notification
✔ Unlock by Volume key.
✔ Support auto enable with start on boot
✔ Simple to use

[Guide User]
✔ Enable Volume Power.
✔ Add the widget to the home screen to use Screen Off.

Note!
✔ This app uses the Device Administrator permission to you can use the shortcut "Screen Off", the notification and the widget to lock the screen

✔ May be you need to wait for a few second to use the app after you kill app.

✔ If you are using widget/shortcut/notification of Volume Unlock to Screen Off. To uninstall the app you can click the button "Uninstall" in-app or go to "System Settings—>Security—>Device Administrators" to uncheck Administrator permission for Volume Unlock and after uninstalling Volume Unlock app same as normal way. If you can't deactivate Device Administrator please try to restart your device to retry or send feedback to me to receive more supports.

If new version, not stable working. You can use the older version. Link download http://goo.gl/Gt1ZjU

Volume Unlock is application free. Setup and enjoy!.
If you like Volume Unlock app don't forget rate 5 stars ★★★★★ or review. They are appreciated for me. Thank you so much

P/s: Communicate google+ groups with me https://plus.google.com/communities/103395796834097167869