Performance and analysis of amorphous silicon p-i-n solar cells made by chemical-vapor deposition from disilane

The photovoltaic performance of amorphous silicon p-i-n solar cells made by chemical-vapor deposition (CVD) from disilane is reported and analyzed. Intrinsic layers were deposited at rates from 0.2 to 50 Å/s at temperatures from 380 to 460 °C with and without boron doping. Device performance was insensitive to substantial differences in disilane purity. A cell efficiency of 4% was achieved. The primary limitation to higher efficiency was low fill factor (<50%) due to high series resistance (>18 Ω cm2). Analysis of the series resistance indicated a contact-related resistance of 4–12 Ω cm2 and a photoconductive resistance composed of intrinsic layer thickness-independent (10 Ω cm2) and thickness-dependent terms. Analysis of the voltage dependence of the current collection indicated a fill factor of 60% would be expected in the absence of series resistance. The maximum short-circuit current of 12.5 mA/cm2 (normalized to 100 mW/cm2) resulted with a boron-doped i layer deposited at 440 °C at 3.3 Å/s. Modeling of the collection efficiency indicated collection widths up to 0.33 μm for boron-doped and 0.24 μm for undoped p-i-n devices. In order to achieve high-efficiency cells using CVD from disilane, the limitations imposed by low photoconductivity, a high density of states, and restricted cell design imposed by the high deposition temperatures would have to be overcome.