1. Electrical Engineering and Computer Sciences; University of California; Berkeley CA 94720 USA
2. Material Sciences Division; Lawrence Berkeley National Laboratory; Berkeley CA 94720 USA
3. Berkeley Sensor and Actuator Center; University of California; Berkeley CA 94720 USA
4. Department of Material Sciences and Engineering; National Chao-Tung University; Hsinchu 300 Taiwan
5. Computer, Electrical and Mathematical Sciences and Engineering Division; King Abdullah University of Science and Technology; Thuwal 23955-6900 Saudi Arabia
6. Department of Materials Science and Engineering; National Tsing Hua University; Hsinchu 30013 Taiwan
7. Joint Center for Artificial Photosynthesis; Lawrence Berkeley National Laboratory; Berkeley CA 94720 USA