IEEE Electrific ation Magazine / ma r c h 201 8 23 + - V EF ph2 h n + n + OH- O2 - h+ H2O H2 (c) O2 e- 2 4 3 OER Metal Anode 1 ~na H2O/O2 H2O Transparent Tunnel Junction (a) p 1.23 V hν > 1.8 eV Vph1 H+ H2/H2O ~nc H2 hν < 1.8 eV Transparent Si Epoxy Au Graded Contact Wafer Buffer Reflector Handle p EVB ECB e- e- HER AM 1.5 Global Tilt Flux dNphdλ (a.u.) (b) (d) Electrochemical Cells Electrical Connection NiBi CPV Modules vard University (Cox et al. 2011, Noorden 2011). (Photo courtesy of the National Academy of Science.) (c) An organic/inorganic perovskite solar cell-based PV-EC system suggested by the Gratzel group (Luo et al. 2014). (Image courtesy of Science.) (d) A PV-EC system constructed by a light concentrator, multijunction PV, and membrane electrode assembly-based EC system (Nakamura et al. 2015). (Photo courtesy of the Japanese Society of Applied Physics.) Figure 3. A PV-EC system developed by various research groups. (a) A PV-PEC cell system developed by the NREL (Young et al. 2017). (Image courtesy of Nature.) (b) The artificial leaf suggested by Har- Potential (V) GalnP Electrolyte Eg = 1.8 eV eV GalnAs Eg = 1.2 eV NiMoZn