Solution‐Processable Conjugated Polymers as Anode Interfacial Layer Materials for Organic Solar Cells

Abstract

With appropriate charge transport layers, one can rationally engineer the driving force, which generally refers to the built-in electric field in devices, so that electrons and holes can be effectively extracted to their respective electrodes, and thereby maximize the efficiency of OSCs. [4] There are two main types of charge transport materials that are commonly used in OSCs: anode interfacial layer (AIL) materials for hole collection and electron transport layer (ETL) materials for electron collection. However, at present, the development of AIL materials is comparatively lagging, as compared to ETL materials. For ETL materials, many materials, such as low-work-function metal, [5] small-molecule organic compounds, [6] nonconjugated and conjugated polymers, [7] and transition metal oxides (TMO), [8] have been proven effective in improving the electron collection efficiency in OSCs. In sharp contrast, only a few materials, such as poly(3,4ethylenedioxythiophene): (styrenesulfonate) (PEDOT:PSS) [9] and MoO 3 , [10] have been extensively used as AILs in OSCs. Generally, the AIL serves two functions: 1) Improving the selectivity and efficiency of hole transport and collection. First, by using AILs, the work function (W F ) of the anode can be effectively enhanced, which helps to construct a built-in electric field in the device with the combination of a low-W F cathode. The built-in electric field provides the fundamental driving force that transfers holes to the anode, where the holes are subsequently collected (Figure 1a). [11] Second, with the modification of the AILs, the W F of the anode can be enhanced to be higher than the positive integer charge-transfer state (E ICT + ) of the donor, in which case the Fermi-level pinning to the E ICT + level occurs to reduce the hole collection barrier at the anode interface (Figure 1b). [12] Third, AILs should effectively block the electrons, reducing the charge recombination at the interface. [13] 2) Improving the physical contact between the anodes and the active layers. With the modification of AILs, the hydrophilic surface of anodes can be changed, which enhances the wettability and film quality of the active layers deposited on the anode surfaces. Moreover, the anode surface can be smoothed by an AIL to passivate surface defects and pinholes, which decreases the leakage current of the OSC devices. To efficiently realize the above functions, AIL materials should possess several characteristics, including a high W F value, exceptional optical transparency, excellent hole In recent years, solution-processed conjugated polymers have been extensively used as anode interfacial layer (AIL) materials in organic solar cells (OSCs) due to their excellent film-forming property and low-temperature processing advantages. In this review, the authors focus on the recent advances in conjugated polymers as AIL materials in OSCs. Several of the main classes of solution-processable conjugated polymers, including poly(3,4-ethylenedioxythiophene):(styrenesulfonate), polyaniline, polyt...

Solution‐Processable Conductive Organics via Anion‐Induced n‐Doping and Their Applications in Organic and Perovskite Solar Cells

“…Among them, some active layers have already reached near 100% internal quantum efficiencies for the conversion of absorbed photons to photogenerated carriers . In such devices, the properties of interfacial materials become more influential, even deterministic to the overall performances of OSCs and PVSCs …”

“…It is because n-doping requires molecular dopant possessing high-lying HOMO (or In such devices, the properties of interfacial materials become more influential, even deterministic to the overall performances of OSCs and PVSCs. [9,[29][30][31][32][33][34][35][36] Although some classical metal oxides, such as zinc oxide (ZnO), titanium oxide (TiO x ), and tin oxide (SnO x ), are widely used in OSCs and PVSCs as interfacial materials, [37][38][39][40][41][42][43] they, however, typically require harsh preparation for improving crystallinities, and therefore charge mobilities, which have difficulty being compatible with low-temperature processed devices, for example, flexible optoelectronics with plastic substrates. Besides, metal oxides possess intrinsic lattice defects, which could trap free charges to induce carrier recombination loss of devices.…”

Solution‐Processed Molybdenum Oxide with Hydroxyl Radical‐Induced Oxygen Vacancy as an Efficient and Stable Interfacial Layer for Organic Solar Cells

“…The advances in photoactive material synthesis and engineering led to a breakthrough in increasing OSC power conversion efficiency (PCE), and recently PCEs exceeding 15% have been reported . Along with the enhancement of PCEs, various efforts, such as the modification of photoactive materials, introduction of additives, and interface engineering by improving the properties of the interfacial layer (IL), have been devoted for improving the operational stability of the completed solar cells, as well as further enhancing device efficiency …”

“…[8,9] Along with the enhancement of PCEs, various efforts, such as the modification of photoactive materials, introduction of additives, and interface engineering by improving the properties of the interfacial layer (IL), have been devoted for improving the operational stability of the completed solar cells, as well as further enhancing device efficiency. [10][11][12] The demand for a highly efficient and stable IL, acting as an electrode modifier and charge-transporting layer, led to the development of various types of ILs including conducting polymers, self-assembled monolayers, conjugated polyelectrolytes, and metal oxides. [13][14][15][16][17][18][19] To date, a large number of studies for cathode ILs have been undertaken, whereas relatively few studies were reported for anode ILs, which simultaneously serve as good efficiency enhancers and stabilizers.…”

Synergetic Effect of Perfluorooctanoic Acid on the Preparation of Poly(3,4‐ethylenedioxythiophene): Lignosulfonate Aqueous Dispersions with High Film Conductivity

“…Since PEDOT:PSS was invented by Bayer AG company in 1994, it has been widely applied as conductive film in organic optoelectronic devices, electrochemical energy conversion and storage devices, biosensors, thermoelectric devices, etc. [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] The conductivities of the most widely used Clevios P VP AI 4083 and PH1000 are between 10 À 3 -10 À 4 and 0.2-1 S⋅cm À 1 , respectively. However, owing to the high difficulty in the design and synthesis of polymeric dopants, only a limited amount of PEDOT:PSS alternatives have been reported.…”