Nitrogen doped chalcopyrites as contacts to CdTe photovoltaics

Abstract

CuInSe 2 , CuGaSe 2 , and alloys thereof produced by a hybrid sputtering and evaporation method show evidence of being dopable with nitrogen by the replacement of some of the Ar sputtering gas with N 2 . This results in a decrease in resistivity of the films with increasing N 2 pressure in the sputtering gas. No doping of AgInSe 2 or CuAlSe 2 has been observed to date following similar methods of deposition. The films are now being tested as back contacts to CdTe solar cells. To date only high resistance contacts have been obtained but more testing and improved CdTe cleaning techniques are required to obtain optimized contacts. The doped chalcopyrites represent potential materials for tunnel junctions for use in CIGS photovoltaics and other devices.

Novel Contact Materials for Improved Performance CdTe Solar Cells Final Report

“…Final Status Summary: A series of experiments on CuInSe2 and AgInSe2 were grown. [1] [2] Due to problems with reproducibility of doping of these materials, CuGaSe2 and various sulfides and oxides were not explored. Amorphous Si was considered in analogy to the HIT contacts to Si solar cells but the hydrogen in the material was thought to degrade the CdTe devices and no satisfactory contact was obtained.…”

“…However, during this period it as discovered that FeS2 was potentially of interest. [4][5][6] Failure of both of the following would suggest a no-go decision: (1) inability to demonstrate nitrogen doping of chalcogenide semiconductors, (2) Preliminary work on pyrite back contacts at UT motivated continuing study of this material in Phase II (see next section). The work on thin film Si:H back contacts was discontinued in Phase II due to the instability of the resulting back contacts.…”

“…[4,6,11] [10] The other materials tested did not produce good contacts. [1][2][3] [2] We developed improved methods for process control and monitoring during deposition of the materials we tested. [7,16] We showed that we could determine the current flow pathways in CdTe devices using scanning microwave impedance microscopy, which advances the general understanding of the devices [13,14].…”