DOE/SERI Polycrystalline Thin-Film Photovoltaic Research

This paper presents recent results, status, and future prospects for the U.S. Department of Energy's (DOE's) Polycrystalline Thin Film Photovoltaic Program, managed by the Solar Energy Research Institute (SERI). The devices being studied most intensively are heterojunctions based on CulnSe2 and on CdTe. Both materials have attained over 10% efficiency in polycrystalline form. The main emphasis ison CulnSe2, for which Boeing has reported an 1196-efficient device (AMI ELH simulation). Important work is being done on studies of the composition/electronic properties of CulnSe2 and its response to post-deposition annealing. In the CdTe research, ohmic, stable back-contacting and control of p-type doping are being investigated. New efforts to study polycrystalline two-junction stacked cellsare underway with two-terminal cells (at IEC) and with four-terminal cells (at SMU). This preliminary work is expected to be expanded, with emphasis on CdTe and other top-cell (high-bandgap) materials. These efforts introduce a number of new research areas (e.g., transparent ohmic contacts to p-CdTe and sub-bandgap light-losses in polycrystalline materials). The aim of the program is to producestable, high-efficiency (15%), thinfilm cells that can be deposited inexpensively by techniques that are scalable to large areas.