Howard Zolla

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 .

Design tradeoffs for beyond 20 Gb/in.2: Using a merged notched head on advanced low noise media (invited)

Design considerations for areal densities beyond 20 Gb/in.2 are discussed, and in particular a demonstration at 24.8 Gb/in.2 is shown. The demonstrations used a single combined write and read head (Merge, Notched head). In this article we will discuss the tradeoffs in kilobytes per inch (KBPI) and tracks-per-inch in obtaining areal densities at 25 Gb/in.2 densities. The KBPI is limited by both the total signal-to-noise ratio and the nonlinear-transition shift. Simple estimates of the increase in channel performance from class IV partial response (PR4), extended partial response 4 (EPR4), and modified EEPR4, as well as the addition of codes which eliminate bit shift and tribit errors are discussed as large contributors to the increase in the areal density.

Spinstand demonstration of areal density enhancement using two-dimensional magnetic recording (invited)

Exponential growth of the areal density has driven the magnetic recording industry for almost sixty years. But now areal density growth is slowing down, suggesting that current technologies are reaching their fundamental limit. The next generation of recording technologies, namely, energy-assisted writing and bit-patterned media, remains just over the horizon. Two-Dimensional Magnetic Recording (TDMR) is a promising new approach, enabling continued areal density growth with only modest changes to the heads and recording electronics. We demonstrate a first generation implementation of TDMR by using a dual-element read sensor to improve the recovery of data encoded by a conventional low-density parity-check (LDPC) channel. The signals are combined with a 2D equalizer into a single modified waveform that is decoded by a standard LDPC channel. Our detection hardware can perform simultaneous measurement of the pre- and post-combined error rate information, allowing one set of measurements to assess the absolute areal density capability of the TDMR system as well as the gain over a conventional shingled magnetic recording system with identical components. We discuss areal density measurements using this hardware and demonstrate gains exceeding five percent based on experimental dual reader components.

Thermal And Electrical Reliability Of Dual-stripe MR Heads

Dual-Stripe Magnetoresistive heads are subjected to accelerated life tests through elevated temperature and excess current. The time to failure is well described by the Arrhenius model, yielding an activation energy of 1.99/spl plusmn/0.11 eV. Extrapolation of the time to failure (TTF) of the total head population to nominal operating conditions yields a mean TTF (MTTP) well in excess of the 1 Mhr called for in high performance applications. Based on these measurements, calculated annual failure rates (AFR) in the ppm/year range are expected over a nominal field service period of 10/sup 5/ hours (11 years).

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.

Influence of magnetic properties of shields on recording head instability parameters

We report on the origin and the influence of small variations in magnetic properties of magnetically soft Sendust films, used as a bottom shield in magnetoresistive heads, on instability parameters probed by quasi-static measurements. A strong correlation of the shields magnetic characteristics with the average wafer asymmetry range is found. The variations in magnetic properties are directly connected with local anisotropy effects as revealed by Kerr microscopy. A direct correlation of the domain structures at the shields surface with microstructure of the film is found. The magnetic domains display a change of magnetics with film growth. The deviations of magnetic properties are due to small structural Sendust changes.

Influence of weak magnetic out-of-plane anisotropy in magnetic shields on recording head instability parameters

In this paper, we report on the origin and the influence of small changes in magnetic properties of magnetically soft Sendust films, used as a bottom shield, on instability parameters derived from quasi-static measurements.