Kim W. Mitchell

Progress towards high efficiency thin film CdTe solar cells

Abstract This paper describes work investigating high rate cadmium telluride (CdTe) film deposition by close-space vapor transport, leading to 4 cm 2 tin oxide/CdTe solar cells of efficiency greater than 10%. Under a 100 mW cm −2 air mass 1.5 global spectrum, a cell of efficiency 10.5% had a short-circuit current of 28.1 mA cm −2 , an open circuit voltage of 0.663 V and a fill factor of 0.563. Our major achievements include (1) the use of completely non-vacuum processing, (2) the fabrication of simple transparent conductive oxide/CdTe cells without need of a CdS window layer, and (3) screenprinted back contacts.

CuInSe/sub 2/ cells and modules

Recent CuInSe/sub 2/ photovoltaic technology advances are discussed. 14.1% active area efficient test cells and the fabrication of monolithic integrated modules with power outputs of 112 W/m/sup 2/ on 940 cm/sup 2/ and 91.4 W/m/sup 2/ on 3900 cm/sup 2/ have been achieved. Packaged modules are stable outdoors. Studies indicate a recombination controlled junction mechanism and imply a wide CIS compositional range over which high-efficiency junctions are possible. Processing improvements already demonstrated on test cells and 940 cm/sup 2/ modules will yield 52-W, 3900-cm/sup 2/ CIS modules. >

Single and tandem junction CuInSe/sub 2/ cell and module technology

A ZnO/thin CdS/CuInSe/sub 2/ (CIS) cell and a 10.5 W, 938 cm/sup 2/ 55-cell CIS module with a 11.2% aperture area efficiency are reported. Other devices include 10% efficient ZnO/thin ZnSe/CIS and 7.3% efficient ZnO/thin CdS/CuInS/sub 2/ cells. A four-terminal 15.6% efficient semitransparent thin-film silicon:hydrogen alloy (TFS)/CIS tandem cell and a 12.3% aperture area efficient TFS/CIS module are also demonstrated. Insight into the factors affecting their performance is provided by modeling and analysis of modules and test structures.<<ETX>>

EBIC analysis of CuInSe2 devices

Abstract This paper describes the electron-beam-induced-current (EBIC) technique and its application to the characterization of CuInSe 2 thin film solar cells. The collected current generated by a scannig electron microscope electron beam can be used to determine spatial non-uniformities, localized defects, p-n junctions, minority carrier lifetimes and diffusion lengths in solar cells. Spatial EBIC images permit detailed examination to 5000X magnification compared with 50X for optical-beam-induced current (OBIC) images.

7.3% efficient CuInSe/sub 2/ solar cell

A 7.3%, 3.3 cm/sup 2/ active area efficient ZnO/thin CdS/CuInS/sub 2/ solar cell is demonstrated with 22.7 mA/cm/sup 2/ J/sub sc/, 592 mV V/sub oc/, and 0.546 fill factor. X-ray diffraction shows that the CuInS/sub 2/ films with are predominantly randomly oriented chalcopyrite CuInS/sub 2/ with additional minor phases such as In/sub 2/S/sub 3/ and Cu/sub 2-x/S present. Optical transmission and reflection data for CuInS/sub 2/ films on glass are also shown. Optical transmission implies a 1.4-eV bandgap, less than the 1.55-eV bandgap for single-crystal CuInS/sub 2/, but consistent with other reported thin-film results. It is concluded that the resolution of several materials, device, and fabrication issues will result in efficiencies of greater than 15%.<<ETX>>

Device analysis of CuInSe/sub 2/ solar cells

Analyses are presented of greater than 12% efficient ZnO/thin CdS/CIS devices, focusing on spectral response and light and dark current-voltage (I-V) over a broad range of intensities (0.64-100 mW/cm/sup 2/) and temperatures (100-300 K). Other measurements presented include voltage-dependent spectral response, capacitance-conductance versus voltage, frequency, temperature, and CIS film and contact resistance. It is found that recombination controls device performance above 200 K and tunneling and series resistance dominate low-temperature device behavior. 14.1%, 3.5 cm/sup 2/ active area cell and 11.2%, 938 cm/sup 2/ module aperture area efficiencies are reported.<<ETX>>

Device aspects of multijunction photovoltaic module research

Abstract Multijunction modeling of single-crystal cells and of polycrystalline and thin film Si:H alloy (TFS) cells is outlined. A number of module design considerations are pointed out. The concept of an ARCO hybrid tandem TFS/-CuInSe 2 module is presented, showing a laboratory demonstration of a 4 cm 2 cell with 13.1% efficiency, and projections of module efficiencies of 15% – 20% are made.