An air-stable inverted photovoltaic device using ZnO as the electron selective layer and MoO3 as the blocking layer

Abstract

An air-stable photovoltaic device based on znic oxide nanoparticles (ZNP) in an inverted structure of indium tin oxide (ITO)/ZnO/poly (3-hexylthiophene) (P3HT): [6,6]-phenyl C 61 -butyric acid methyl ester (PCBM)/MoO 3 /Ag is studied. We find that the optimum thickness of the MoO 3 layer is 2 nm. When the MoO 3 blocking layer is introduced, the fill factor of the devices is increased from 29% to 40%, the power conversion efficiency is directly promoted from 0.35% to 1.27%.The stability under ambient conditions of this inverted structure device much is better due to the improved stability at the polymer/Ag interface. The enhancement is attributed to the high carriers mobility and suitable band gap of MoO 3 layer.Organic solar cells (OSCs) have been deeply investigated recently due to their commercial applications and simple methods of preparation by coating and printing methods [1, 2] , The conventional solar cells based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C 61 -butyric acid methyl ester (PCBM) with power conversion efficiency (PCE) of 4%-5% have been reported [3][4][5] . But without encapsulation, these devices always exhibit poor lifetimes, because acidic polymer layer which included ploy (3,4-ethlendioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) can react with metal electrode and alter its properties. In addition, the cathode with low work function is oxidized easily by oxygen and moisture in air [6][7][8] .According to the problems, the inverted organic solar cells (inverted-OSCs), in which the positions of the anode and cathode are reversed, have been demonstrated [9,10] . The devices can be used in air stably, and use the high work function metal as electrode and the metal oxide (TiO 2 , ZnO) as the electron acceptors at the ITO side. The inverted-OSCs have many advantages, such as higher stability and more convenient preparation. In addition, the higher concentration of acceptors balances the rate of diffusion of holes and electrons, which can give a promising route to improve the efficiency [9][10][11] .Recently, zinc oxide (ZnO) as the electron selective or hole blocking layer has been introduced into OSC devices because of its high electron mobility and facile synthesis. The morphology of ZnO has also been modified from a thin film to nano-ridges by controlling the annealing process [12,13] .However, the performance of inverted-OSCs is still restricted by architecture. For example, the PEDOT:PSS layers are demonstrated to reduce the diffusion of oxygen to the active layer effectively, but it degrades the performance of the device due to chemical reaction with metal electrode. Some reports have shown that MoO 3 can be used as the hole selective layer, so to deposite a MoO 3 layer before anode metal may improve the stability of the interface [14][15][16] .The ZnO-based inverted solar cells are fabricated, and MoO 3 lavers with different thicknesses deposited to achieve the optimum performance of the devices. The air stability of the inverted devices are compared with that of the conventi...

Air-Stable Efficient Inverted Polymer Solar Cells Using Solution-Processed Nanocrystalline ZnO Interfacial Layer

“…MoO 3 is chosen as the hole transport layer (HTL) due to its favorable energy level alignment with the HOMO level of P3HT. There have been reports using the same material components, − but the PCE of 3.7% obtained in this work is the highest thus far. Moreover, the use of such crystalline ZnO NP interfacial layer can avoid the high temperature post annealing process widely adopted for the sol–gel derived ZnO interfacial layer, hence to bypass the ETL electrode damaging issue during this annealing step …”

Application of quinoline derivatives in third-generation photovoltaics

“…The second electrode is usually made of metal [57][58][59]. To improve the efficiency of the cells, some additional materials are used between the electrodes to block the electrons [60][61][62] or to block the holes [63][64][65][66]. The function of the material, however, is not predefined; for example, supporting materials can be used as electrodes.…”