Abstract
We present a method of ozonation to form the rear-side passivation layers of crystalline silicon PERC cells. In the method, a thin aluminum film was deposited on the back surface of a silicon wafer and then was oxidized into an aluminum oxide layer by gaseous ozone. Lifetimes of the wafers with such passivation layers proved to be increased with respect to those untreated, and the resultant PERC cells showed a performance improvement compared with standard cells with full back surface fields.
Highlights
A basic cell structure of crystalline silicon PERC cells commonly fabricated by industry is shown in Figure 1 [1], where silver electrodes are screen printed on the front surface of a p-type textured wafer with an antireflection coating (ARC) and a diffused N+ layer, while local contacts are formed by fired aluminum paste at the laser-ablated parts of the back surface with a stack of AlOx/SiNx
A local back surface fields (BSFs) is formed on the rear contact to facilitate the collection of holes, and the thin AlOx layer contributing field-effect passivation will eject electrons and reduce recombination of electrons and holes near the rear side of the wafer [2]
The resultant passivation layer AlOx is formed at the interface of Si/Al2O3 after the wafer is annealed at a proper temperature and produces negative charges with a density that is several times as high as 1012 cm-2
Summary
A basic cell structure of crystalline silicon PERC (passivated emitter and rear cell) cells commonly fabricated by industry is shown in Figure 1 [1], where silver electrodes are screen printed on the front surface of a p-type textured wafer with an antireflection coating (ARC) and a diffused N+ layer, while local contacts are formed by fired aluminum paste at the laser-ablated parts of the back surface with a stack of AlOx/SiNx. The inventors of [14] proposed spraying methanol solution containing aluminum elements (or containing aluminum acetylacetonate) on the surface of a silicon wafer for forming a passivation layer This idea could result in a tremendous reduction in manufacturing cost, leaving unsolved a problem of uneven thicknesses of the passivation layers from sample to sample. In this new method, a thin aluminum film was first deposited on the back surface of a phosphorus-diffused silicon wafer and oxidized into an aluminum oxide layer by gaseous ozone. A thin aluminum film was first deposited on the back surface of a phosphorus-diffused silicon wafer and oxidized into an aluminum oxide layer by gaseous ozone Such an aluminum oxide layer proved to produce a good level of passivation after annealed at a proper temperature. Experimental results for minority carrier lifetime and cell performance measurements are presented in Section 3, followed by a conclusion section
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