(554c) Back Contacted Three Dimensionally Structured Electrodeposited Chalcogenide Solar Cells

Three dimensionally (3D) structured photovoltaic devices have received considerable attention as a means to improve thin film device efficiency through more effective light management and decoupling of charge transport from photon absorption. Herein, three dimensionally structured CdS/CdTe and CdSe/CdTe thin film photovoltaic devices based on interdigitated arrays of microscale electrodes are examined.  This geometry eliminates front contacts and window layers enabling absorption in the UV region as well as the visible portion of the solar spectrum.  Electrodeposited CdTe/CdSe heterojunction devices demonstrate moving the window layer behind the absorber permits materials with smaller bandgaps than CdS to be effectively utilized.  In these structures the electrode height orthogonalizes carrier collection from light absorption.  External quantum efficiencies (EQE) were modeled for several electrode dimensions (pitch, width, height) and carrier lifetimes to fully capture the advantage of this geometry.  Experimental results demonstrate significantly improved performance with increased grain size or annealing temperature.  Pt and Ir contacts are examined showing Pt electrodes react with the absorber while Ir electrodes are stable under thermal processing conditions, addressing challenges of electrode reactivity.  Although electrode differentiation requires a selective technique such as electrodeposition, the test bed structures and absorber synthesis processes are amenable to an array of deposition techniques for fabrication and measurements of three dimensionally structured semiconductors, contact materials and photovoltaic devices.