W. A. Anderson

An 8% efficient layered Schottky‐barrier solar cell

An 8.1% efficient 1‐cm2 Schottky‐barrier solar cell has been fabricated in our laboratory using a layered Schottky barrier on 2‐Ω cm p‐type silicon. Reproducible results have been obtained on the layered structure which involves 44‐A Cr adjacent to the silicon to obtain good photovoltaic voltage and a 58‐A Cu overlayer to decrease cell resistance. The layered structure provides good control of barrier height, resistance, and optical transmission. Application of this approach should produce a 15% efficient Schottky solar cell and be readily applied to thin‐film silicon solar cells when high‐quality thin silicon films have been developed.

High‐efficiency Cr‐MIS solar cells on single and polycrystalline silicon

Cr‐MIS solar cells having a 2‐cm2 area have been fabricated to produce 12.2% efficiency on single crystal and 8.8% efficiency on polycrystalline Si. Surface‐state data were used to predict open‐circuit voltages of 0.60 and 0.50 V, respectively, for the single‐crystal and polycrystalline Si. Spectral response measurements and Cr metal thickness confirm the differences in short‐circuit current density using these two types of Si.

Temperature effects in Schottky‐barrier silicon solar cells

Experimental results are reported concerning temperature effects from 25 to 125u2009°C on Schottky‐barrier solar cells which were fabricated using a semitransparent Cu/Cr barrier metal layer on p‐type silicon. The open‐circuit voltage decreased by 2.3 mV/°C and the fill factor by 0.11%/°C, while the short‐circuit current increased slightly with increased temperature. These results are consistent with previous work on p‐n–junction silicon solar cells. The diode quality factor n was shown to decrease with increased temperature, as predicted by field emission theory. The room‐temperature photovoltaic output of cell 96 remained at 0.54 V, 25.4 mA/cm2, and 8.5–10.6% efficiency using 80–100‐mW/cm2 sunlight illumination after repeated temperature cycling.

Barrier height modification in silicon Schottky (MIS) solar cells

A study of experimental data on Cr-oxide-p-Si solar cells has led to a metal evaporation procedure which gives 0.50 V < Voc< 0.56 V. This voltage is independent of the method used in oxide formation when oxide thickness ranges from 10 to 30 Å. It is concluded that slow deposition of the Cr on an oxide interface leads to a lowered metal work function and thus an increased Voc. A high n-value and fixed charge in the oxide are not necessary to obtain a high Voc.

Schottky barrier diodes for solar energy conversion

Several Schottky barrier solar cells were fabricated by evaporation and sputtering of Al ohmic contacts and Cr or AuCr alloy barrier metals on 0.5-10.0 2 Ω ċ cm p-type silicon. Potential efficiencies of 4.8 to 12 percent were observed which would be realized with improved fill factors. Computer studies of the optical problem indicate an output power increase by a factor of four through the use of reduced barrier metal thickness (from 275 to 100 A) and alloy barrier metals to more effectively transmit solar energy to the Schottky junction.

Thin metal films as applied to Schottky solar cells: optical studies

Thin metal films ( approximately 100 A) have been studied for application to Schottky barrier solar cells (SBSC). Metal films having >55% transmission over the solar spectrum and resistance of 20 ?/? have been applied to Si to form a rectifying contact. A 9.5% sunlight efficient SBSC was produced using 50-A Cr adjacent to the Si for good adhesion and high open circuit voltage and a 50-A Cu overlayer to produce low sheet resistance. Film quality has been related to evaporation rate, metal layer selection, and substrate conditions. Solar cell performance is determined by the transmission and resistance of the thin metal films. Spectral response data show the SBSC to exhibit improved short wavelength sensitivity compared to the p-n Si solar cell.

Auger, ellipsometry, and environmental studies of thin films applied to schottky (MIS) solar cells

Schottky (MIS) solar cells typically consist of the structure 5Å Cr/50Å Cu/40Å Cr/20Å oxide/silicon. A study of metal diffusion and precise oxide thickness is important to predict the stability of such a device. Devices fabricated using the same process are shown to have almost identical electronic performance. Auger profiles show that the metal films do not penetrate through adjacent regions except when Ag is used in place of Cu. Ag does penetrate through the Cr and into the Si which alters the electronic properties. Ellipsometer studies show the insulator to range in thickness from 20Å to 28Å which may be controlled by variation of the heat-treatment cycle. Environmental studies of encapsulated solar cells show that polystyrene offers more protection than Sylgard l84. Failures due to dirt coatings, discoloration, thermal stresses, poor wire bonds, voltage degradation, and fill factor degradation have been observed. Properly fabricated and encapsulated cells have performed well for more than a year. A hermetic encapsulation may be necessary for future long term stability.

Spectral‐response and diffusion‐length studies of amorphous, polycrystalline, ribbon, epitaxial, and single‐crystal silicon MIS solar cells

Spectral‐response and diffusion‐length characteristics of the various MIS cells developed at Rutgers and previously reported in the literature have been investigated. The cells, designated according to the type of Si substrate used, appear in the following descending order based on the above studies: (1) Monsanto single‐crystal Si with a peak quantum efficiency (QE) of 87.4% and a diffusion length (Ln) of 70 μm, (2) Wacker polycrystalline Si, peak QE=82.8%, Ln=60 μm, (3) IBM ribbon Si, (4) epitaxial Si, (5) Mobil‐Tyco EFG ribbon Si, and (6) amorphous Si (Plasma Physics Corp.). Theoretical plots of quantum efficiency and short‐circuit current density are shown to be in reasonable agreement with experimental results. The enhanced ultraviolet response of the MIS cell compared to that of a commercial N/P junction cell is demonstrated even though the latter device has a peak QE of almost 100% and an Ln value of 184 μm. The spectral studies lend support to the conclusions derived from the previously measured el...

Proton radiation effects on Cr‐MIS single‐crystal Si solar cells

Cr‐MIS solar cells on single‐crystal Si, with a 2‐cm2 area and approximately 10% efficiency, have been subjected to 1.0‐ and 1.6‐MeV proton radiation at total dosages of up to 3.3×1013 p/cm2. Photovoltaic studies reveal characteristic short‐circuit current and open‐circuit voltage degradation similar to proton‐irradiated junction‐type solar cells. (See H. Y. Tada and J. R. Carter, Solar Cell Radiation Handbook, JPL Publication 77‐56, 1977.) Spectral response measurements reveal output decay primarily due to minority‐carrier diffusion‐length decreases of up to 96%.

Comparing Radiation Effects in Gunn and Impatt Diodes

Several Gunn and IMPATT diodes were subjected to neutron and gamma radiation while in oscillation. This provided data which could not be obtained by diode testing after irradiation. Non-passivated IMPATT diodes were most tolerant of neutron fluence effects. Gunn diodes were insignificantly influenced by this radiation flux but failed at lower fluence levels than did the IMPATT diodes.