Do you have the screen set to maximum brightness? I have been outside on a completely cloudless, sunny November day and been able to read my screen.
When you pull the toolbar down from the top of the screen, there is a slider. Slide that all the way right.
Or, if you have the power control as one of your widgets, the button on the far right is a circle that looks like the sun. Tap that once and it fills halfway. Screen is at half brightness. Tap that again and the center is completely filled. That is full brightness.
If you still can't see after that, you may have a hardware issue. I have to use full brightness outdoors, but the screen is clear as day on a day that is clear as... well... day.