Thin-Film CIGS Photovoltaic Technology: Annual Technical Report, Phase II, 16 April 1999-15 April 2000

A summary of Energy Photovoltaics' Phase II work includes the following: 1) EPV has demonstrated that it can sputter a Mo back-contact capable of supporting very high efficiency cell processing. Using EPV Mo, NREL has deposited a 17.1% CIGS cell (no AR coating). EPV believes it can identify the signature of 'good' Mo. The Mo was produced on EPV's 0.43 m2 pilot-line equipment; 2) EPV has performedcompound synthesis for several classes of materials, namely non-Cu precursor materials, Cu-containing materials, and ternary buffer materials. Using a ternary compound synthesized at EPV (ZIS) as an evaporation source material for the buffer layer, a Cd-free CIGS device has been produced having an efficiency of 11.5% (560 mV, 32.1 mA/cm2, FF 64.3%). The ZIS films are photoconductive, and thedevices exhibit no dark-light crossover or light soaking effects; 3) EPV initiated the interest of the University of Oregon in capacitance spectroscopy of CIGS devices. An Urbach tail with characteristic energy E0 < 20meV was identified by transient photocapacitance spectroscopy; 4) Small-area CIGS devices were produced in the pilot-line system with an efficiency of 12.0% (581 mV, 30.1 mA/cm2,FF 68.7%), and in an R&D-scale system with 13.3% efficiency (569 mV, 34.1 mA/cm2, FF 68.1%); 5) An improved linear evaporation source for Cu delivery has been developed and was used for CIGS formation in the pilot-line system. The deposition width is 45 cm. This technological 'tour de force' allows EPV to build large-area CIGS systems possessing considerable flexibility. In particular, bothEPV's FORNAX process and NREL's 3-stage process have been implemented on the pilot line. A CIGS thickness uniformity of ? 7% over a 40 cm width has been achieved; 6) A 4-head linear source assembly was designed, constructed, and is in use. Flux monitoring is practiced; 7) Large-area CIGS modules were produced with Voc's up to 36.3 V; 8) EPV has started to construct an entirely new CIGS pilotline for scale-up and limited manufacturing purposes. The coating width will be 65 cm; 9) The company's analytical capabilities are currently being upgraded with the installation of ICP and SEM/EDS facilities.