The "micromorph" solar cell: extending a-Si:H technology towards thin film crystalline silicon

Abstract

Recent progress of solar cells based

In situ silicon oxide based intermediate reflector for thin-film silicon micromorph solar cells

“…To overcome this issue, an intermediate reflecting layer ͑IRL͒ can be introduced between the two cells to increase the current of the top cell. 2 For an intermediate layer to act as a reflector, its refractive index n must be lower ͑typically n IRL Ϸ 2͒ than that of silicon ͑n Si = 3.8 at 600 nm͒ such as to produce a refractive index step that causes the reflection of light at the material interface. The layer which serves as IRL is required to be sufficiently conductive to avoid blocking current and as transparent as possible to minimize the current losses due to absorption of light outside the active layers.…”

“…In the first attempts to realize this intermediate reflector, zinc oxide ͑ZnO͒ has been used. [2][3][4] In a recent study, the top-cell current could be increased by 2.8 mA/ cm 2 , using a 110-nm-thick ZnO IRL with a 180-nm-thick top cell. 3 When considering industrialization, there are, however, two main drawbacks of ZnO-based IRL: the need for an additional ex situ deposition step and an additional laser scribe for monolithic series interconnection to avoid lateral shunting of solar module segments.…”

The “Micromorph” cell: a new way to high-efficiency-low-temperature crystalline silicon thin-film cell manufacturing?

“…Apart from few isolated papers (3-5), µc-Si:H was in the past generally not seriously taken into account as a candidate for becoming an active semiconductor for solar cells. The novel inputs that have lead to the successful use of µc-Si:H in solar cells as reported in recent work (1,(6)(7)(8)(9), can be reduced to two main characteristics:…”

“…Due to this fact, the top cell produces, within the micromorph tandem cell, two thirds of the total power of the cell (9). Because of this, the stability of the top cell will remain a key feature as long as the open circuit voltage of the bottom cell remains limited to such low values: One may conclude that a further increase of the V oc -value of the bottom cell alone is the most important individual factor for further improvement in the stable efficiency of the micromorph cell.…”

N-I-P Micromorph Solar Cells on Aluminium Substrates

“…These so-called 'micromorph' cells are 'real' tandem cells, employing two materials of a different optical gap for the top and the bottom cell (1.7eV and 1eV, respectively [2]). The enhanced infrared absorption and the lack of light-induced degradation [3] of the microcrystalline silicon are successfully combined with the high V oc of the amorphous silicon solar cell.…”