An all-solid-state perovskite-sensitized solar cell based on the dual function polyaniline as the sensitizer and p-type hole-transporting material

Highlights

• Polyaniline with brachyplast structure was electropolymerized and characterized.

• The polyaniline acted as the sensitizer and p-type HTM for the ass-PSSC.

• The ass-PSSC delivered a photovoltaic conversion efficiency of 7.34%.

• The ass-PSSC demonstrated a good long-term stability after 1000 h.

Abstract

High performance dual function of polyaniline (PANI) with brachyplast structure is synthesized by using a two-step cyclic voltammetry (CV) approach onto the fluorinated tin oxide (FTO) glass substrate, which acts as the sensitizer and p-type hole-transporting material (p-HTM) for the all-solid-state perovskite-sensitized solar cell (ass-PSSC) due to its π–π* transition and the localized polaron. The ass-PSSC based on the PANI delivers a photovoltaic conversion efficiency of 7.34%, and reduces from 7.34% to 6.71% after 1000 h, thereby 91.42% of the energy conversion efficiency is kept, indicating the device has a good long-term stability.

Introduction

Dye-sensitized solar cells (DSSCs) have attracted scientific and technological interest of researchers in the past decades as a high efficiency and low-cost alternative to conventional silicon p–n junction photovoltaic devices [1], [2], [3]. This kind of device based on a dye-sensitized porous nanocrystalline TiO₂ photoanode, an iodine-based liquid electrolyte, and a platinum counter electrode in a sandwich-like architecture, allowed an achievement of the efficiency of up to 12.3% [2]. Recently, a new class of hybrid organic-inorganic perovskite compounds (CH₃NH₃PbX₃, X = I, Br and Cl) replace the traditional dye (N719) as light harvesters for solar cells due to their direct band gap, wide light-absorption, and high carrier mobility [4], [5], [6], [7], [8], [9], [10]. The perovskite-sensitized solar cell (PSSC) presents an impressive high open circuit voltage and realizes an all-solid-state solar cell by replacing the liquid electrolyte with a hole transporting material (HTM) for the production and stability of the photovoltaic device [11], [12].

The most commonly used HTM is 2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9′-spiro-biuorene (spiro-MeOTAD) [4], [5], [6], [7], [8], [9], [10], which demonstrates low recombination rate, efficient charge transport, and also good pore filling of the TiO₂ layer improving device performance. Of course, poly-triarylamine (PTAA) [5], poly(3-hexylthiophene) (P3HT) [13] are also used as the HTMs. However, Z. Ku et al. reported on carbon counter electrode in perovskite-based solar cells without HTMs, and achieved an efficiency of 6.64% [14]. For the sake of low cost, good stability, and simple easy preparation of designable structures, the p-type conducting polymers, e.g., polypyrrole (PPy) [15], polyaniline (PANI) [16], [17], and poly(3,4-ethylenedioxythiophene) (PEDOT) [18], [19], [20] have been employed as cheaper alternatives in all-solid-state DSSCs. Among them, PANI has already been reported as a cost-effective and stable p-type HTM (p-HTM) and sensitizer in a solid-state DSSCs [16], [17]. For instance, Tan et al. reported on the polyaniline as a hole transport material to prepare solid solar cells [16]. Senadeera et al. were successful at depositing PANI via molecular self-assembly on TiO₂ and using as a sensitizer in the solid-state solar cell [17].

It is well known that the PANI can be easily prepared through chemical polymerization [21] and electropolymerization methods [22], [23], [24], [25], [26], [27], [28], [29]. The electropolymerization methods are considerably simpler and more cost-effective technique to obtain conducting polymers with the controllable surface morphology and well adhesion on the substrate surface. The reported electropolymerization methods used in synthesizing PANI include: the cyclic voltammetry (CV) [22], [23], constant potential [24], [25], constant current [26], pulse current [27], and pulse potentiostatic [28] methods. Recently, we investigated a two-step CV approach for the preparation of PANI, which quickly yielding high performance PANI with brachyplast structure [29].

Therefore, by considering these facts, here we report on an all-solid-state perovskite-sensitized solar cell (ass-PSSC) based on the PANI with brachyplast structure as the p-HTM, which was quickly electropolymerized by using the two-step CV method onto the fluorinated tin oxide (FTO) glass substrates. In addition, the PANI also acted as a function of sensitizer enhancing the device performance. Thus the ass-PSSC assembled with the PANI electrode exhibited a superior photovoltaic conversion of 7.34%, and showing a good long-term stability.