Obtaining a higherVoc in HIT cells

Abstract

We have achieved a very high conversion efficiency of 21Á5% in HIT cells with a size of 100Á3 cm 2 . One of the most striking features of the HIT cell is its high opencircuit voltage V oc , in excess of 710 mV. This is due to the excellent surface passivation at the a-Si/c-Si heterointerface realized by Sanyo's successful technologies for fabricating high-quality a-Si films and solar cells with low plasma damage processes. We have studied ways to treat the surface to produce a good interface throughout our fabrication processes. We have also investigated the deposition conditions of a-Si layers for optimizing the barrier height for the minority carriers in the heterojunction. Our approach for obtaining HIT cells with a high V oc is reviewed here.

Heterojunction Silicon Microwire Solar Cells

“…The low thermal budget process of depositing a-Si layer on c-Si, while a fabrication advantage, in general, could be of particular interest in the case of lower purity and high defect silicon material, as it may avoid the possibility of defect activation after prolonged high temperature excursion. We also found the fabricated devices in this particular case showed no sensitivity to the back passivation that is present in a standard HIT device, 22 which is due to the short carrier diffusion length in the start material compared to the wafer thickness. Finally, 200 nm aluminum doped zinc oxide (AZO) and 800 nm aluminum were sputtered as the front transparent conductive oxide (TCO) and the back-contact of the device.…”

“…With the increased area of the vertical junction, the saturation current is greatly affected by junction characteristics and the surface recombination at the outer wall of the wire. 8 Heterojunction of crystalline silicon (c-Si) and wider bandgap amorphous silicon (a-Si) with a thin intrinsic layer in between, known as HIT structure pioneered by Sanyo, 22 is recognized to result in cells with very low saturation current. The structure consists of n-type crystalline base and p-type amorphous emitter layer, with an intrinsic a-Si layer in between.…”

Mobility dependent efficiencies of organic bulk heterojunction solar cells: Surface recombination and charge transfer state distribution

“…Even if current surface recombination velocities may be closer to infinity than to zero, it is certainly possible to decrease surface recombination currents by using band offsets for the respective minorities at the contacts. This concept has been known for a long time in photovoltaics 33 and has been applied in both inorganic 34,35 and organic devices. 36 …”

Nature of doped a-Si:H/c-Si interface recombination

“…4 Experimentally, however, such layers have been found to result sometimes in poorer electronic passivation of c-Si surfaces than their intrinsic counterparts. [5][6][7] For this reason, typically, a few nanometer thin intrinsic buffer layer is inserted between the c-Si surface and the doped a-Si: H films for device fabrication. 8 For HJ solar cells featuring such stacked film structures, impressive large area ͑Ͼ100 cm 2 ͒ energy conversion efficiencies ͑Ͼ22%͒ have been reported.…”