As poor stability is the primary constraint for the commercialization of perovskite solar cells, improving stability has been the primary focus of recent research works regarding solar cells that make use of perovskite materials. Different metal oxide transport layers are being used with the aim of fabricating stable perovskite solar cells. A stable and efficient solar cell with both metal oxide transport layers (ZnO and N i O X ) and a perovskite (methyl ammonium lead iodide) absorber layer is simulated in this work, and a comparison of performance parameters is made with other transport layers from the literature. The issue of optimization regarding the thickness of the absorber layer and the doping concentration in the absorber and transport layers has been addressed, and the effect of defect concentration at the interface has been investigated. Optimum performance is achieved with an absorber layer of thickness 800 nm. Linear grading is also introduced in the absorber layer by varying the concentration of different halides, which increases the efficiency by approximately 8% owing to the increase in the short circuit current density.

Ultra-violet (UV) light emitting diodes operating at 339 nm using transparent interband tunnel junctions are reported. Tunneling-based ultraviolet light emitting diodes were grown by plasma-assisted molecular beam epitaxy on 30% Al-content AlGaN layers. A low tunnel junction voltage drop is obtained through the use of compositionally graded n and p-type layers in the tunnel junction, which enhance hole density and tunneling rates. The transparent tunnel junction-based UV LED reported here show a low voltage drop of 5.55 V at 20 A/cm2 and an on-wafer external quantum efficiency of 1.02% at 80 A/cm2.

In this work, we demonstrate for the first time two-junction ultraviolet light emitting diodes enabled by transparent tunnel junctions. Low voltage-drop tunnel junctions were realized in Al0.3Ga0.7N layers through a combination of high doping and compositional grading. Capacitance and current-voltage measurements confirmed the operation of two junctions in series. The voltage drop of the two-junction LED was 2.1 times that of an equivalent single-junction LED, and the two-junction LED had higher external quantum efficiency (147%) than the single junction.

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