| 초록 |
Inorganic-organic hybrid perovskite has been receiving spotlight as a solar absorbing layer and it has already achieved an over 21% power conversion efficiency. Perovskite solar cells exhibit exceptionally high open-circuit voltage (Voc)—with Voc deficit (difference between bandgap and Voc) typically being smaller than 500 mV—which means they should make good light emitting diodes as well. Methylammonium lead bromide perovskite (MAPbBr3) has a band gap about 2.3 eV, which is suitable for the emission of green light. Using MAPbBr3 as an active layer, we have fabricated devices using two different architectures—standard (n-i-p) and inverted (p-i-n) structures. The standard device structure consists of ITO/Comact-TiO2/mesoporous TiO2 (n)/MAPbBr3 (i)/Spiro-OMeTAD (p)/Au and the inverted device structure consists of ITO/PEDOT:PSS (p)/MAPbBr3 (i)/PCBM (n)/Al. Standard devices under illumination exhibit a well rectifying behavior with Voc reaching as high as 1.22 V, but no emission is observed when current was injected under dark (i.e., LED mode). By contrast, the inverted devices show electroluminescence with green light, but they exhibit a Ohmic behavior with Voc at 1.41 V. We explain the different device behaviors between the two different structures with energy band alignment that determines the carrier injection energy barrier. Further improvement in luminescence by replacing the layers surrounding the MAPbBr3 active layers will be discussed. |
