On the morphology of polymer‐based photovoltaics

Abstract

We review the morphologies of polymer-based solar cells and the parameters that govern the evolution of the morphologies and describe different approaches to achieve the optimum morphology for a BHJ OPV. While there are some distinct differences, there are also some commonalities. It is evident that morphology and the control of the morphology are important for device performance and, by controlling the thermodynamics, in particular, the interactions of the components, and by controlling kinetic parameters, like the rate of solvent evaporation, crystallization and phase separation, optimized morphologies for a given system can be achieved. While much research has focused on P3HT, it is evident that a clearer understanding of the morphology and the evolution of the morphology in low bad gap polymer systems will increase the efficiency further. While current OPVs are on the verge of breaking the 10% barrier, manipulating and controlling the morphology will still be key for device optimization and, equally important, for the fabrication of these devices in an industrial setting.

Mixing in PCBM/P3HT bilayers, using in situ and ex situ neutron reflectivity

“…A long-established and well-studied choice for such a blend consists of a fullerene derivative and a conjugated polymer. 5,6 Here, the BHJ consists of a complex morphology that is designed to enable efficient separation of charges at the interface between the electrondonating polymer and the electron-accepting fullerene. 7 The requirement for large interfacial area needs to be balanced by the provision of a continuous path for electron and hole transport.…”

“…It is hoped that the development of further understanding of the morphology of OPV materials in thin-film architectures will underpin the successful commercial application of OPVs. 2,5,10,11 This paper describes a study that focusses on conjugated polymer/fullerene mixing, by looking at the evolution of morphology within a simplified (bilayer) geometry, as a function of the polymer film thickness and temperature.…”

Morphological Control Agent in Ternary Blend Bulk Heterojunction Solar Cells

“…Therefore, the BHJ solar cell to date holds the leading PCE values of OPV system around 7%-11% in lab-scale and takes the majority of OPV studies [1]. Some important subjects regarding the advance of OPV over the past decades can be referred to the comprehensive review articles, i.e., materials development [2][3][4][5], morphology [1,[6][7][8][9][10], device physics [11][12][13][14], device structure [15].…”

“…Various strategies have been reported to tailor the morphology from local-scale (molecular ordering/conformation) to global-scale (domains/networks in tens and hundreds of nanometer) e.g., thermal annealing [16][17][18][19], solvent vapor annealing [17,20], type of processing solvents [21], incorporation with solvent additives [1,22], etc. These morphological control methods and associated characterization techniques have also been comprehensively reviewed [1,[6][7][8][9][10]23,24]. In our previous review article, we systematically summarized the effects of incorporating solvent additives which has found to be effective in a variety of BHJ systems [1].…”

Perovskite-polymer hybrid solar cells with near-infrared external quantum efficiency over 40%

“…Solution-processed polymer solar cells utilizing conjugated polymer and PCBM bulk-heterojunction (BHJ) blend as a light absorber are also a promising photovoltaic technology due to tunable absorption features and energy levels, as well as excellent solution processibility of the diverse polymers [20−29]. Therefore, integrating the advantages of both photovoltaic technologies into a simple photovoltaic device will be of great importance to achieve cost-effective and low temperature processed photovoltaic technologies.It is well-established that nanoscale bicontinuous interpenetrating networks in polymer:PCBM BHJ solar cells are beneficial for realizing efficient exciton dissociation and charge transport [30,31]. Very recently, researchers from polymer solar cell community have introduced feasible strategies to push forward planar junction perovskite/ fullerene solar cells [32−36] In the past several years, conjugated polymers and organometal halide perovskites have become regarded as promising light-absorbing materials for next-generation photovoltaic devices and have attracted a great deal of interest.…”