D. Willett

The effects of sweep rate, voltage bias and light soaking on the measurement of CIS-based solar cell characteristics

Recent work by several groups has shown that the efficiency of CuInSe/sub 2/ (CIS) solar cells often increases after light soaking. The authors have found that the voltage sweep rate may also have a large effect on the measured fill factor. This complicates the accurate measurement of the performance of CuInSe/sub 2/ and other I-III-VI/sub 2/ solar cells. Devices would have to be pre-light soaked and tested only under constant illumination with a slow voltage ramp rate to most closely simulate a module in operation.<<ETX>>

CuInSe2 photovoltaic modules

Abstract This paper reviews the status of CuInSe 2 (CIS) module development. The potential of CIS for high power, thin film photovoltaic modules is demonstrated by the achievement of 14.1% active area cell efficiencies and unlaminated module power outputs of 10.5 W (11.2% aperture efficiency) on 940 cm 2 modules and 37.8 W (9.7% aperture efficiency) on 3900 m 2 modules. The definition of 0.4 m 2 CIS module pilot production is progressing.

Recent Advances in Single-Junction and Tandem Thin Film Modules Based On CuInSe2

Advances in the CuInSe2 (CIS) photovoltaic technology continue to increase large-area module efficiencies while demonstrating the application of low cost production-compatible processing techniques. Single-junction large area (0.4 m2) unencapsulated modules have been fabricated with aperture area efficiencies over 10%. Key issues addressed to achieve this performance were shunts related to localized defects and patterning, thin film uniformity across large substrates, and the improvement of macroscopic mechanical adhesion at the CIS/Mo interface.

Progress in CIS-based module development

Alloys of copper indium diselenide are the most promising candidates for reducing the cost of photovoltaics below the cost of crystalline silicon. Small area, fully integrated modules exceed 13% in efficiency and long-term outdoor stability has been demonstrated. The availability of natural resources and environmental impacts appear acceptable. Challenges remain to scale the process to larger area and to pass accelerated environmental testing. Process scale-up is systematically proceeding from the foundation of a reproducible small area module process with low variation; however, large-area circuit performance has not yet achieved the same level as the baseline process. Differences in performance between the baseline and large area processes have been isolated to differences in the equipment used to form absorbers and is the subject of current development. The impact of larger part size has been tested for each process step using the demonstrated baseline process. Results indicate that larger-area parts w...

Advances in large-area Si:H thin film modules

Recent advances in processing large-area modules using thin-film Si:H (TFS) alloys have yielded an 8.4% aperture area efficiency and 33.2 W on a an unlaminated and unframed 0.4 m/sup 2/ module. Film uniformity and shunting are major impediments to the manufacture of large TFS modules. Large-area modules are more sensitive than small laboratory devices to debris and contamination that cause shunting. Several major sources of shunts have been identified and controlled. These include substrate contamination, laser patterning debris, and airborne particulates. It is pointed out that further improvements can advance module performance to 10% aperture efficiency and 38 W.<<ETX>>

Results of recent CuInSe/sub 2/ module investigations

Efforts in large-area CuInSe/sub 2/ module development have focused on simplified, low-cost processing options with improved yield and performance. A large area (3890 cm/sup 2/), 40.8 W, 10.5% aperture area efficiency module has been demonstrated. Durable module performance, as indicated by over 40 months of continuous outdoor exposure at the National Renewable Energy Research Laboratory PV Outdoor Test Facility, has been shown. Two alternate interconnect structures, designed to simplify processing, have been used to fabricate small-area modules of 10.3% and 11.7% efficiency. Transparent conducting films of ZnO:Al, 1.5 /spl mu/m thick, have been sputter deposited at rates greater than 3 nm/sec with bulk resistivities of 1.5/spl times/10/sup -3/ /spl Omega/-cm, and cell efficiencies greater than 10% on 100 cm/sup 2/ substrates have been achieved using this ZnO. Alternate absorber layer formation and substrate selection have led to a 2.5 percentage point increase in average cell performance and a narrower power distribution of these cells. These improvements have resulted in a 3.1 cm/sup 2/ active area device with 15.1% efficiency.<<ETX>>

Progress in large-area CuInSe/sub 2/ thin film modules

Prototype modules of CuInSe/sub 2/ (CIS) have been fabricated with efficiencies that exceed 10%. The challenge is to improve the processing yield of these modules to that suitable to advance to pilot manufacturing. A number of analytical tools have been developed to provide insight into the loss mechanisms in these large-area monolithic structures. Techniques for characterizing the adhesion of the semiconductors, the device quality, the interconnect quality, and the film uniformity are discussed. Improvements in adhesion have eliminated the primary cause of mechanical failure, leading to tighter module efficiency distributions.<<ETX>>

CuInSe/sub 2/ module environmental durability

Stability of CuInSe/sub 2/ (CIS) modules through outdoor testing and accelerated environmental testing has been demonstrated on 0.4-m/sup 2/ modules. Package durability has been demonstrated for 0.4-m/sup 2/ laminates with polyurethane frames. Although stability has been demonstrated, a distribution of results is common with power changes ranging from slight gains to losses greater than 10%. Correlations and distinctions between the distributions for outdoor and accelerated environmental testing are discussed. During accelerated environmental testing, temperature effects, alone, rather than temperature combined with humidity, cause changes in power. An interaction between CIS and the package is not necessary to cause these changes in power.<<ETX>>

The Effect of Localized Defect Features on CuInSe2 Device Performance

A wide variety of analytical tools support the investigation of large area (0.4 m2) CuInSe2 (CIS) module development at Siemens Solar Industries. Small devices are sliced out of large area plates and studied using light and dark I-V and spectral response. Optical and electron micrographs characterize surface features and interfaces. These micrographs in conjunction with optical beam induced current (OBIC) images provide a detailed picture of the device response topography. Optical and electron micrographs of devices reveal no surface features or pinholes that correlate to the low output OBIC spots. However, tests reveal a high correlation of low adhesion and the low OBIC spots. These results guide the optimization of large area deposition and patterning equipment and procedures.

41.5 watt, 10.5% Si:H/CuInSe/sub 2/ tandem thin film modules

Thin-film tandem modules using semitransparent Si:H alloy (TFS) and CuInSe/sub 2/ (CIS) component circuits show promise of achieving high photovoltaic performance using low-cost thin-film processing. TFS/CIS (thin-film Si:H/CuInSe/sub 2/) tandem modules with 41.5 W and 10.5% aperture efficiency on 0.4 m/sup 2/ areas have been demonstrated. Film deposition and patterning processes have been successfully extended to 0.4 m/sup 2/ substrates. The larger size is comparable with conventional single-crystal silicon commercial modules and represents a prototype high-efficiency thin-film power product. The performance characteristics of the individual CIS and TFS cells and submodules and of the tandem TFS/CIS cells and modules are described.<<ETX>>