THREE DIMENSIONALLY STRUCTURED INTERDIGITATED BACK CONTACT THIN FILM HETEROJUNCTION SOLAR CELLS
C.M. Hangarter1, B.H. Hamadani2, J.E. Guyer1, H. Xu2,3, R. Need1, and D. Josell1
1. Metallurgy Division, Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg , MD 20899
2. Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, MD 20899
3. Maryland NanoCenter, University of Maryland, College Park, MD 20742.
Three dimensionally structured thin film photovoltaic devices based on interdigitated arrays of microscale electrodes are examined by EQE simulations, indicating considerable JSC enhancement is possible through elimination of the front contact and window layer required in planar geometry devices. Electrode parameters including, pitch, width, height, and material are modeled and experimentally probed, demonstrating experimentally and capturing in models dependence on intrinsic material properties and electrode dimensions. In contrast to analogous silicon wafer back contact solar cells where the electrodes are placed on the silicon absorber at the end of processing, in this design the semiconductor is deposited on the electrodes, taking advantage of the thin film processing already required. Electrodeposited CdS/CdTe heterojunction devices approach 1% efficiencies with simulations as well as optical measurements indicating significant potential for improvement. Suboptimal performance is attributed to unintended materials reactions that preclude annealing at the temperatures required for absorber optimization as well as Schottky barrier formation on the nonoptimal electrode materials. 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 subject to processing feasibility and materials compatibility.