Temperature dependence of protocrystalline silicon/microcrystalline silicon double-junction solar cells

We have investigated the temperature dependence of hydrogenated protocrystalline silicon (pc-Si: H) /hydrogenated microcrystalline silicon (gc-Si:H) double-junction solar cells. A boron-doped zinc oxide (ZnO:B) film is employed as an intermediate layer between the pc-Si:H top cell and the gc-Si:H bottom cell. The fabricated solar cells exhibit good stability against light soaking. Photocurrent density-voltage (photo J-V) characteristics are measured under AM 1.5 illumination at ambient temperatures in the range of 25-75 degrees C. The double-junction solar cells show a temperature coefficient (TC) for conversion efficiency (eta) of around -0.30 to -0.45%/degrees C, which between the TC for eta of the pc-Si:H top and gc-Si:H bottom cells. It is found that the values of TC for eta are inversely proportional to the initial open-circuit voltage (V-oc). In contrast, these values become higher with the increase in the crystalline volume fraction (X-c) of the i-mu c-Si:H in the bottom cells. Since the pc-Si:H/mu c-SiM double-junction solar cells exhibit high eta, low light-induced degradation, and low temperature dependence, they are good candidates for solar cells that operate in high-temperature or tropical regions.