(34f) Charge Separation in Extremely Thin Absorber Solar Cells

Extremely thin absorber (ETA) solar cells utilize a very thin light-absorbing layer at the nanostructured interface between n- and p-type semiconductors to enable efficient separation of photoexcited charge carriers.  The high-area interface allows smaller absorber thicknesses to harvest the same amount of light as thicker planar cells.  Because the absorber is thin, efficient charge separation can be achieved with material of lower electronic quality, which enables low-cost processing and new materials not possible with planar cells.  Here we report on our recent efforts to understand and control interfacial electron and hole transfer in ETA cells consisting of ZnO/CdSe/CuSCN and ZnO/CdSe/electrolyte, in both nanowire-based and planar configurations. Nanowire arrays provide large surface area and conduits for 1-D electron transport, while planar cells provide simplified geometry for model studies.  Our approach utilizes a combination of solar cell measurements and ultrafast transient absorption spectroscopy to understand the effects of CdSe thickness, annealing conditions, and interfacial treatments on the dynamics and efficiency of charge carrier separation, and ultimately on the solar-to-electric energy conversion efficiency.  These studies provide guidelines for architecture design and materials selection for ETA solar cells.