All-room-temperature solution-processed new nanocomposites based hole transport layer from synthesis to film formation for high-performance organic solar cells towards ultimate energy-efficient fabrication

It is an ultimate goal of energy-efficient fabrication that photovoltaic devices only need low energy consumption processes covering both synthesis of material and fabrication of device. Regarding to charge transport layer, it is worthwhile to synthesize nanomaterials and deposit films all at room temperature while still have good electrical properties. Meanwhile, there are very limited studies on room temperature solution approaches for modification on nanocrystal colloidal for facilely forming high quality film with tunable electrical properties. In this work, we propose and demonstrate a new nanocomposites of maghemite and iron hydroxide through a low energy consumption approach which is all room-temperature solution processes from the synthesis of the nanocomposites to the formation of high quality hole transport layer (HTL). Strategically adjustment of acidity for the conversion of prepared precipitation is demonstrated to achieve a component controllable maghemite and iron hydroxide nanocomposites which contributes to in-situ tunable work function of the nanocomposites HTL from 4.70 eV to 5.16 eV. Simultaneously, since the nanocomposites synthesized from this approach have the features of ultrasmall size of 6-10 nm and surfactant-free, high quality and efficient HTL films can be formed at room temperature. For organic solar cells using nanocomposite as HTL, the power conversion efficiency can be significantly improved by as much as 80% as compared with the optimized devices without HTL. Besides, both the efficiency and stability of the nanocomposite based organic solar cells are better than that of devices using poly (3,4-ethylenedioxythiophene): poly(styrene-sulfonate) (PEDOT:PSS). Consequently, the work contributes to the fabrication of simple, low-cost, and stable optoelectronics promoting green photovoltaics and flexible electronics.