Harin S. Ullal

Cu (In,Ga)Se2 thin films and solar cells prepared by selenization of metallic precursors

CuIn(1−x)GaxSe2 (CIGS) thin films with Ga ratio, x, ranging from 0.55 to 0.75 were grown on Mo/glass substrates by the selenization of metallic precursors in a H2Se atmosphere. Without a postdeposition annealing step the films were found to have a highly graded composition that became Ga rich near the absorber/Mo interface. A high‐temperature annealing step promoted diffusion of Ga to the surface region of the films. These absorbers were used to fabricate glass/Mo/CIGS/CdS/ZnO thin‐film solar cells with open‐circuit voltages ranging from 0.4 to 0.74 V and efficiencies approaching 12%. Devices, as well as the absorber layers, were characterized.

Current status of polycrystalline thin-film PV technologies

Thin-film solar cell technologies based on CdTe and CIS have made significant technical progress. Most of the improvements have occurred at the level of solar cells, modules, systems, and reliability testing in both CdTe and CIS. Total-area efficiencies of 14.7% for a thin-film CdTe solar cell deposited on a low-cost, sodalime glass fabricated by Golden Photon, Inc. was verified by NREL. Siemens Solar Industries has fabricated a world-record, aperture-area efficiency of 11.1% and a power output of 40.6 W for a thin-film CIGSS module. Solar Cells, Inc. has fabricated a large-area, thin-film CdTe module with an aperture-area efficiency of 9.1% and power output of 61.3 W; Golden Photon, Inc., has also fabricated a power module with an aperture-area efficiency of 9.2% and power output of 31.0 W. Key research issues for CdTe and CIS are discussed in this paper. Several polycrystalline thin-film arrays based on CdTe and one based on CIGSS have been deployed worldwide. Stability data indicated by both thin-film CIS and thin-film CdTe modules and systems are encouraging. Many companies worldwide are actively pursuing early commercialization efforts based on both speciality products and power modules.

Progress and issues in polycrystalline thin-film PV technologies

Substantial progress has occurred in polycrystalline thin-film photovoltaic technologies. However, the transition to first-time manufacturing is still under way, and technical problems continue, This paper focuses on the promise and the problems of the copper indium diselenide and cadmium telluride technologies, with an emphasis on continued R&D needs for the near-term transition to manufacturing and for next-generation improvements. In addition, it highlights the joint R&D efforts being performed in the US Department of Energy/National Renewable Energy Laboratory Thin-Film Photovoltaic Partnership Program.

Polycrystalline thin film photovoltaics

Significant progress has recently been made towards improving the efficiencies of polycrystalline thin-film solar cells and modules using CuInSe/sub 2/ and CdTe. The history of using CuInSe/sub 2/ and CdTe for solar cells is reviewed. Initial outdoor stability tests of modules are encouraging. Progress in semiconductor deposition techniques has also been substantial. Both CuInSe/sub 2/ and CdTe are positioned for commercialization during the 1990s. The major participants in developing these materials are described. The US DOE/SERI (Solar Energy Research Institute) program recognizes the rapid progress and important potential of polycrystalline thin films to meet ambitious cost and performance goals. US DOE/SERI is in the process of funding an initiative in this area with the goal of ensuring US leadership in the development of these technologies. The polycrystalline thin-film module development initiative, the modeling and stability of the devices, and health and safety issues are discussed.<<ETX>>

“The role of polycrystalline thin-film PV technologies in competitive PV module markets”

This paper discusses the developments in thin-film PV technologies. It provides an outlook on future commercial module efficiencies achievable based on todays knowledge about champion cell performance. It also provides a relative cost comparison of thin-film and wafer/ribbon based Si PV modules. In 2007, about 65% of the modules produced in the US were thin-film modules when amorphous silicon modules are also considered.

Polycrystalline Thin-Film Photovoltaics: From the Laboratory to Solar Fields

We review the status of commercial polycrystalline thin-film solar cells and photovoltaic (PV) modules, including current and projected commercialization activities

POLYCRYSTALLINE THIN FILM PHOTOVOLTAIC TECHNOLOGY

Polycrystalline thin-film materials based on copper indium diselenide (CuInSe2, CIS) and cadmium telluride (CdTe) are promising thin-film solar cells for various power and specialty applications. Impressive results have been obtained in the past few years for both thin-film copper indium gallium diselenide (CIGS) solar cells and thin-film CdTe solar cells. NCPV/NREL scientists have achieved world-record, total-area efficiencies of 19.3% for a thin-film CIGS solar cell and 16.5% for thin-film CdTe solar cell. A number of technical R&D issues related to CIS and CdTe have been identified. Thin-film power module efficiencies up to 13.4% has been achieved thus far. Tremendous progress has been made in the technology development for module fabrication, and multi-megawatt manufacturing facilities are coming on line with expansion plans in the next few years. Several 40-480 kW polycrystalline thin-film, grid-connected PV arrays have been deployed worldwide. Hot and humid testing is also under way to validate the long-term reliability of these emerging thin-film power products. The U.S. thin-film production (amorphous silicon[a-Si], CIS, CdTe) is expected to exceed 50 MW by the end of 2005.Polycrystalline thin-film materials based on copper indium diselenide (CuInSe2, CIS) and cadmium telluride (CdTe) are promising thin-film solar cells for various power and specialty applications. Impressive results have been obtained in the past few years for both thin-film copper indium gallium diselenide (CIGS) solar cells and thin-film CdTe solar cells. NCPV/NREL scientists have achieved world-record, total-area efficiencies of 19.3% for a thin-film CIGS solar cell and 16.5% for thin-film CdTe solar cell. A number of technical R&D issues related to CIS and CdTe have been identified. Thin-film power module efficiencies up to 13.4% has been achieved thus far. Tremendous progress has been made in the technology development for module fabrication, and multi-megawatt manufacturing facilities are coming on line with expansion plans in the next few years. Several 40-480 kW polycrystalline thin-film, grid-connected PV arrays have been deployed worldwide. Hot and humid testing is also under way to validate the long-term reliability of these emerging thin-film power products. The U.S. thin-film production (amorphous silicon[a-Si], CIS, CdTe) is expected to exceed 50 MW by the end of 2005.

The DOE/SERI polycrystalline thin film subcontract program

The authors give a summary of the status of polycrystalline thin film solar cells. The requirements for them to meet the Department of Energy (DOE) cost-competitive goals, program highlights, research issues, manufacturability, and future plans are presented. A table showing funding for polycrystalline thin films is also given.<<ETX>>

Polycrystalline thin-film photovoltaic technologies: from the laboratory to commercialization

Substantial technical progress has occurred in the area of polycrystalline thin-film photovoltaic technologies based on cadmium telluride (CdTe) and copper indium gallium diselenide (CuInGaS/sub 2/, [CIGS]) in the past few years. We report here the many technical advances made in the area of materials research, device development, manufacturing technology, module and system deployment and testing, and early commercialization activities worldwide related to CdTe and CIGS products for specialty and power applications. Also, the various technical issues related to CdTe and CIS are elucidated. NREL scientists have achieved record total-area efficiency of 15.8% for a novel thin-film CdTe solar cell, and world-record total-area efficiency of 18.8% has been achieved fora thin-film CIGS, solar cell. Details of cell processing are given. World-record power output of 915 W and aperture-area efficiency of 10.6% have been achieved by BP Solar, Fairfield, California for a thin-film CdTe power module. Also, a world-record aperture-area conversion efficiency of 12.1% for a thin-film CIGSS power module fabricated by Siemens Solar Industries, Camarillo, California. Both efficiencies and power outputs have been independently confirmed by NRFL.

Properties of Cd and Zn partial electrolyte treated CIGS solar cells

We study the influence of Cd partial baths on the photovoltaic properties of CuInGaSe/sub 2/ (CIGS) and CuInGaSSe/sub 2/ (CIGSS) thin film absorbers. We find that efficient solar cells can be fabricated by this treatment, and we compare their properties; with those containing CdS window layers grown by chemical bath deposition. The results suggest that Cd plays a dominant role in establishing efficient photovoltaic junctions in Cu InSe/sub 2/ alloys. Micron scale photoluminescence scans show non-uniformity along the length probed. Cd treatment quenches one of the luminescence transitions, which indicates a change in shallow acceptor level density. We present a model that helps to explain the evolution of photovoltaic action.