Organic solar cells with room-temperature solution processed metal oxides as carrier transport layers

Abstract

With the rapid development of renewable energy techniques, organic solar cells (OSCs) have been recognized as promising candidate for addressing global energy crises. The attractive advantages of low-cost, light-weight, solution process and flexibility can be feasible for large-area solar energy applications. Recently, OSCs have been achieved with power conversion efficiencies (PCE) over 10%. Compared to traditional inorganic solar cells, OSCs are still facing challenges of realizing high-efficiency, easy-fabrication and long-lifetime for practical solar energy applications.

To be cost competitive in the fabrication of high-performance OSCs, solution-processed metal oxides have been introduced to function as hole and electron transport layers (HTL and ETL) between active layer and electrodes. It has been shown to have competent efficiency and stability compared to the traditionally used hole and electron transport materials such as poly(3,4-ethylenedioythiophene):poly (styrenesulfonate) and calcium. While metal oxide films are mostly deposited by thermal evaporation methods under high vacuum conditions or solution processed with high temperature annealing treatment, our works focus on room-temperature solution processed metal oxides functioning as efficient carrier transport layers in OSCs.

The detailed works are listed below: 1. Room-temperature solution processed molybdenum oxide as hole transport layer (HTL) in OSCs

In this work, room-temperature solution processed molybdenum oxide (MoOx) is proposed and demonstrated to function as efficient HTL in OSCs. Meanwhile, this approach can feature in water-free film formation processes with low boiling point solvent. Introducing silver nanoparticles (Ag NPs) to form Ag NP-MoOx composite film can further enhance the performance of OSCs. By incorporating the composite HTL, inverted OSCs with PCE of 7.94% can be achieved.

2. Over 1.1 eV work function tuning of intercalated metal oxides as both ETL and HTL in OSCs with normal and inverted structures

We propose one type of metal oxide functioning as carrier transport layers in OSCs with large work function tuning ability. The cesium intercalation method is demonstrated to work well with molybdenum oxide and vanadium oxide. OSCs based on cesium (Cs) intercalated metal oxides show efficient performance and good adaptability in both normal and inverted devices.

3. OSCs using solution processed post-treatment-free nickel oxide nanoparticles as HTL

A facile chemical precipitation method for high-quality non-stoichiometric nickel oxide (NiOx) nanoparticles (NPs) is demonstrated. With proper intrinsic work function of the product, HTL can be formed by spin-casting NiOx NPs without any post treatment. With the analyses of chemical composition and energy band structures, OSCs using NiOx HTL can achieve good optoelectronic performance.

4. High performance OSCs using room-temperature solution processed SWCNT, V2Ox as HTL and ZnO as ETL

The low band gap polymer OSCs based on single wall carbon nanotube (SWCNT) or vanadium oxide (V2Ox) as HTL and ZnO as ETL can exhibit remarkable PCE of 10.55%. By incorporating ZnO as the ETL in OSCs, PCE over 10% can be achieved. The stability of OSCs can be enhanced by using all metal oxides as HTL and ETL. These approaches can offer excellent choices of effective carrier transport layers towards high-performance and long-lifetime OSCs.