James Freitag

Status of electroplating based CIGS technology development

CIGS is the leading thin film PV material in terms of it capability to yield high efficiency solar cells. Co-evaporation method already yielded solar cells with close to 20% efficiency. Despite this success, however, commercialization of CIGS has not been aggressive. One reason for this is the fact that CIGS is a complex material. The other reason is the difficulty of scaling up this technology while keeping the cost structure competitive. SoloPower has developed a low cost electrodeposition-based CIGS technology for large scale roll-to-roll manufacturing. The substrate is a flexible metallic foil. CIGS absorber layers are formed through annealing and thermal activation of electrodeposited precursor layers. Top and bottom contacts are formed by roll-to-roll sputtering approaches. The technique has excellent ability to control the composition of the deposited layers over large are substrates. After forming a roll of solar cells, devices are cut and then packaged in module structures. Flexible solar cells with an area of over 100 cm2 were fabricated with over 12% efficiency. Over 1 m2 area modules with an efficiency of 10% were also fabricated.

Flexible cells and modules produced using roll-to-roll electroplating approach

Thin film Cu(In,Ga)Se2 (CIGS) photovoltaic cells are considered to have a high potential for low cost electricity production due to their demonstrated high conversion efficiencies. Various methods have been used to make thin film CIGS solar cells. In the present approach, a low cost roll-to-roll electroplating process is utilized to deposit the CIGS precursor layers. The electroplating technology provides well controlled composition along the length and width of the flexible substrates demonstrating its suitability as a low cost CIGS precursor deposition method. Precursor layers are then subjected to rapid thermal processing to form a photovoltaic-grade CIGS absorber. The processing is done using roll-to-roll production equipment on a flexible metallic substrate. The CIGS based solar cells are fully finished in roll form and then cut into large area cells. The cells are then interconnected to fabricate panels with about 1.1 m2 aperture area and about 115W power output. These rigid panels show excellent stability under damp heat test conditions and are certified against both UL and IEC standards. More recent work has focused on lightweight flexible solar modules. These modules open new application areas and can further lower the cost of systems by lowering the installation costs. Flexible modules with aperture area efficiency as high as 11.2 % have been demonstrated. Standard module certification tests, including 1000 hour damp heat test, show very small changes of Pmax .

Indoor and outdoor testing of low weight flexible CIGS modules

Some of the critical advantages of the thin films are being light and flexible. These attributes of the thin films can be advantageously realized when thin film CIGS material is formed on flexible substrates such as stainless steel foils. However due to moisture sensitivity of the CIGS solar cells, commercial flexible CIGS modules that can meet the markets requirements and obtain formal certifications have been elusive. In this presentation, work will be presented that will describe the significant progress made in the field of flexible low weight CIGS modules. A significant milestone was reached when the formal certifications to UL 1703, IEC 61646, and IEC 61730 standards were obtained for the first time for flexible CIGS modules. These modules have excellent power levels reaching a 12.1 aperture efficiency as measured at NREL. Many accelerated tests including the damp humidity test (85C and 85% humidity) were performed in excess of 5000 hours. The results show that there is very little change in the Pmax of the modules and that the total power loss after 5000 hours of testing is less than 10%. Further accelerated indoor tests including temperature cycling and humidity freeze will be discussed and the results will be compared against the rigid CIGS modules. After obtaining the formal certifications, the modules were deployed outdoors and grid connected. The flexible CIGS modules perform very well with performance ratios exceeding 0.85. Additional indoor and outdoor test results will be presented.