The incorporation of hole transport materials (HTMs) in perovskite solar cells (PSCs) is crucial to improve the device performance and the operational stability. These materials play a key role because they selectively improve hole transport efficiency, blocks the electron transfer to anode, and avoid degradation at a metal-perovskite interface [1].

A broad number of HTMs (inorganic materials, small molecules and polymers) has been reported and tested in diverse PSC architectures, resulting in different power conversion efficiencies and stabilities [2].

Commercially available PEDOT:PSS is the most commonly HTM used in inverted PSCs as well as in organic photovoltaics. However, this material is very sensitive to humidity, has poor film-forming properties and causes corrosion at the adjacent layers in the device due to the strong acidic nature of polystyrenesulfonate (PSS). Additionally, PEDOT:PSS cannot be optimally integrated in conventional PSC structures (n-i-p) because water strongly degrades perovskite layers. Other alternatives, such as inorganic HTMs possess high hole-mobility and stability, but present some drawbacks in terms of solvent compatibility with the perovskite. Moreover, polymer-based HTMs or small molecules such as spiro-type HTMs have led to remarkable power conversion efficiencies but considerations on costs, processing and stability make researchers to consider other materials [1].

Consequently, there is a need to explore alternative HTMs that combine high photovoltaic performance with low production costs. Furthermore, it is quite challenging the development of HTMs suitable to be incorporated on top of the perovskite layer in conventional PSCs [3].

Here, we present a new generation of transparent conducting materials with suitable characteristics for efficient charge transport in photovoltaic and electroluminescent applications. These materials are synthesized by the in situ oxidative polymerization of EDOT-based monomers and derivatives inside a transparent host polymer. As a result, homogeneous ultrathin films (up to 10 nm) with high transparency (greater than PEDOT:PSS, especially in the NIR) and tunable conductivities from 10-4 to 600 S/cm can be synthesized to successfully fulfill all the specific requirements of any PSC architecture. Besides, our material can be properly formulated with a wide range of solvents to be absolutely compatible with perovskite-based devices. In this work, we will also discuss the optical and optoelectronic characterization and will demonstrate the efficient use of this material as HTM in some perovskite-based devices.

[1] L. Calió, et al., Angew. Chem. Int. Ed. 2016, 55, 14522

[2] Z.H. Bakr, et al., NanoEnergy, 2017, 34, 271-305

[3] Xiaoqing Jiang et al., Scientific Reports, 2017, 7, 42564