n-i-p structure yields high-efficiency solar cells
Researchers at the Institute of Photovoltaics at the Juelich Research Center (Juelich, Germany) have been able to grow low-temperature microcrystalline silicon-carbide (µc-SiC) layers on a low-cost glass substrate to create an n-side illuminated n-i-p solar cell that has significantly higher quantum efficiency (QE) and short-circuit current density than conventional p-i-n solar cells.
The improved performance of the n-i-p solar cell is attributed to two effects: first, higher transparency of the n-type µc-SiC window layers compared to conventional p-type microcrystalline silicon layers, allowing enhanced light penetration through the window layer and a correspondingly higher generation of photocurrent in absorbing layers; and second, high hole-drift mobility in the intrinsic absorbing layer, causing efficient collection of photocurrent. The µc-SiC films were grown using a hot-wire chemical-vapor-deposition process at a substrate temperature of 250°C. Under standard “air-mass 1.5” illumination (equivalent to sunlight at sea level at 48° from the zenith; see www.laserfocusworld.com/articles/286515), the n-i-p solar cells had short-circuit current densities approximately 10% better than comparable p-i-n solar cells. Around 2 µm, one n-i-p cell had a very high QE current density of 26.7 mA/cm2, translating to a 9.1% solar-cell efficiency. Contact Yuelong Huang at [email protected].