Carrier‐Selectivity‐Dependent Charge Recombination Dynamics in Organic Photovoltaic Cells with a Ferroelectric Blend Interlayer

Abstract

research has been successfully conducted to optimize the BHJ-based OPV devices, including the development of new photoactive materials, [11][12][13][14] pre or postproduction treatment methods, [15][16][17][18] and device architectures. [19][20][21][22][23][24][25][26][27][28][29] Especially, in the area of the device architecture optimization, tremendous efforts have been dedicated toward optimizing the electrode interfaces by adjusting the optical modulus [ 19 ] and promoting effi cient charge collection through Ohmic contacts. [30][31][32][33][34][35] Several reports have focused on the "carrier selectivity" at electrodes, which critically determines the photovoltaic performance of devices with non-Ohmic contact electrodes, such as inverted OPVs. [36][37][38] Since the difference in the work functions (WFs) of electrodes is usually not suffi cient to constitute the built-in potential within an inverted OPV device incorporating high work function cathodes such as the Indium Tin Oxide (ITO), the effi cient charge collection in BHJ structures, which bears an intrinsically high probability of unwanted charge recombination near the electrode, must be sought through approaches that block misdirected carriers at the electrode interface. [ 39 ] In this sense, wide bandgap semiconductor materials, such as ZnO, TiO x , MoO 3 , and their composites, have been widely studied as carrier selective layers. [40][41][42][43] However, the complexities of polymer-based blend systems and the indistinct interfaces in the multilayer structures hinder a comprehensive investigation of the charge-collecting interfaces outside of traditional empirical approaches in the respective photoactive layers. Therefore, the development of new device architectures that enable explicit control over the interfaces, as well as an improved understanding of the corresponding device operating mechanism, should be addressed before device performances may be further enhanced.Ferroelectric materials provide an interesting new strategy for precisely controlling the electrical properties of electronic devices. Inorganic ferroelectric materials, such as BiFeO 3 and NaNbO 3 , are frequently introduced to fabricate switchable fi eld-effect photovoltaic devices that enable control over the photovoltage above the bandgap, according to the polarization Interfacial energetics determines the performance of organic photovoltaic (OPV) cells based on a thin fi lm of organic semiconductor blends. Here, an approach to modulating the "carrier selectivity" at the charge collecting interfaces and the consequent variations in the nongeminate charge carrier recombination dynamics in OPV devices are demonstrated. A ferroelectric blend interfacial layer composed of a solution-processable ferroelectric poly mer and a wide bandgap semiconductor is introduced as a tunable electron selective layer in inverted OPV devices with non-Ohmic contact electrodes. The direct rendering of dipole alignment within the ferroelectric blend layer is found to increase the carrier selectivity of t...

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