Fig. 4: Illustration of the evolution of TPC solar cells.

Evolution of the TPC IV parameters from single layer to the double layer, the optimized ITO deposition, and the improvement due to MgF2 antireflection coating. The optimization of the TPC solar cells is along these triangle points. All solar cells have been measured with isolated back contacts of the surrounding cells (more details about the measurement are in Supplementary Discussion 4).