Jicheol Park

Air-stable inverted structure of hybrid solar cells using a cesium-doped ZnO electron transport layer prepared by a sol–gel process

We have developed an air-stable inverted structure of poly(3-hexylthiophene) (P3HT) : cadmium selenide (CdSe) hybrid solar cells using a cesium-doped ZnO (ZnO:Cs) electron transport layer. The ZnO:Cs layer was simply prepared at low temperature by the sol–gel process using a ZnO solution containing cesium carbonate (Cs2CO3). With increasing Cs-doping concentration, the conduction band edge of ZnO is decreased, as confirmed by scanning Kelvin probe microscopy. The energy level of ZnO:Cs is effective for electron transport from CdSe. Consequently, the power conversion efficiency (PCE) of the inverted P3HT : CdSe hybrid solar cells using the ZnO:Cs electron transport layer is 1.14%, which is significantly improved over that (0.43%) of another device without Cs. X-ray photoelectron spectroscopy analysis revealed that the amount of CdSe on the substrate (or the bottom surface) is larger compared with the air (or top) surface regardless of the P3HT : CdSe weight ratio. The vertically inhomogeneous distribution of CdSe in the hybrid solar cells gives better charge transport from CdSe to ZnO:Cs in the inverted structure of the device compared with that in the normal structure. As a result, the inverted hybrid solar cell consisting of 1 : 4 (wt/wt) P3HT : CdSe shows the best efficiency, while the best efficiency of a normal hybrid solar cell is achieved at 1 : 9 (wt/wt) P3HT : CdSe.

Improvement of power conversion efficiency of P3HT:CdSe hybrid solar cells by enhanced interconnection of CdSe nanorods via decomposable selenourea

We introduce a novel method to improve the device performance of P3HT:CdSe hybrid solar cells by using selenourea (SeU) for ligand exchange. SeU induces interconnection of CdSe nanorods in the nanoscale range without severe aggregation. The power conversion efficiency of the devices with SeU is improved from 1.71% to 2.63% due to efficient charge transport through interconnected CdSe nanorods.