Excess Currents in MINP-Type Solar Cells

MINP silicon solar cells with up to 16.5-percent efficiency have been fabricated using an ion-implanted shallow n-layer followed by a 20–25 A insulator and low work-function metal grid. This design reduces surface recombination, suppresses dark current, and gives increased UV spectral response. Current-voltage data, in the dark and under AM1 illumination, have been taken from 90 to 375 K for four different designs. These data lead to determination of the excess-current component which, in some cases, gives a linear semilogarithmic behavior over much of the voltage range and an ideality factor which increases with decreasing temperature. These trends suggest a current component governed by field emission at the MIS interface and on the solar-cell edges. Control of this current in other cells gave great improvement in efficiency. Much of this excess-current component is eliminated by careful attention to the edges of the solar cell, leaving a small field-emission component under the MIS contact. High-efficiency passivated N/P cells show a small recombination component of excess current.