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Metal-insulator-semiconductor back contact has been employed for a perovskite organic lead iodide heterojunction solar cell, in which an ultrathin Al2O3 film as an insulating layer was deposited onto the CH3NH3PbI3 by atomic layer deposition technology. The light-to-electricity conversion efficiency of the devices is significantly enhanced from 3.30% to 5.07%. Further the impedance spectrum reveals that this insulating layer sustains part of the positive bias applied in the absorber region close to the back contact and decreases the carrier transport barrier, thus promoting transportation of carriers. [ABSTRACT FROM AUTHOR]

A spectrum-splitting and beam-concentrating (SSBC) diffractive optical element (DOE) for three-junction photovoltaics (PV) system is designed and fabricated by five-circle micro-fabrication. The incident solar light is efficiently split into three sub-spectrum ranges and strongly concentrated on the focal plane, which can be directly utilized by suitable spectrum-matching solar cells. The system concentration factor reaches 12×. Moreover, the designed wavelengths (450 nm, 550 nm and 650 nm) are spatially distributed on the focal plane, in good agreement with the theoretical results. The average optical efficiency of all the cells over the three designed wavelengths is 60.07%. The SSBC DOE with a high concentration factor and a high optical efficiency provides a cost-effective approach to achieve higher PV conversion efficiencies. [ABSTRACT FROM AUTHOR]