Introduction: Thin Film Photovoltaics

Commercialization of CdTe solar cell technology has been dominated by First Solar, established in 1999 using CdTe technology developed by Solar Cells Inc. As the first to demonstrate the “economy of scale” utilizing high-speed/high-throughput manufacturing processes, their success has spawned several competitors that are now close to bringing large manufacturing facilities online.

The band gap of CdTe is 1.45 eV, a near- perfect match to the AM 1.5 terrestrial spectrum, and thus CdTe solar cells have the highest theoretical solar cell efficiency of any of the thin film technologies. However, since 2001, improvements in champion laboratory cell efficiency have been stagnate at 16.7 percent (NREL), until 2011, when First Solar reported a 17.3 percent efficient cell, representing an improvement of less than 5 percent. The fundamental issue with CdTe solar cells is the low open-circuit voltage that is dominated by space charge recombination. Modifications to the device design and/or control of the CdTe electronic properties will be required to advance the performance of the CdTe solar cells.

In the following article, Michael Bauer, CTO of Calyxo GmbH, presents his view of the present status and future potential of CdTe solar cell technology. The key features of the CdTe solar cells are highlighted and the areas where improvements in device performance can potentially be achieved are discussed. The article presents an optimistic timetable for improving the device performance, particularly for improvements in Voc that are needed to reach efficiencies greater than 20 percent.

FPV7_N_Intro_Birkmire_TFPV.pdf