Recent Advances in Morphology Optimization for Organic Photovoltaics

Abstract

Organic photovoltaics are an important part of a next-generation energy-harvesting technology that uses a practically infinite pollutant-free energy source. They have the advantages of light weight, solution processability, cheap materials, low production cost, and deformability. However, to date, the moderate photovoltaic efficiencies and poor stabilities of organic photovoltaics impede their use as replacements for inorganic photovoltaics. Recent developments in bulk-heterojunction organic photovoltaics mean that they have almost reached the lower efficiency limit for feasible commercialization. In this review article, the recent understanding of the ideal bulk-heterojunction morphology of the photoactive layer for efficient exciton dissociation and charge transport is described, and recent attempts as well as early-stage trials to realize this ideal morphology are discussed systematically from a morphological viewpoint. The various approaches to optimizing morphologies consisting of an interpenetrating bicontinuous network with appropriate domain sizes and mixed regions are categorized, and in each category, the recent trends in the morphology control on the multilength scale are highlighted and discussed in detail. This review article concludes by identifying the remaining challenges for the control of active layer morphologies and by providing perspectives toward real application and commercialization of organic photovoltaics.

Single‐Junction Polymer Solar Cells with 16.35% Efficiency Enabled by a Platinum(II) Complexation Strategy

“…In terms of active blend morphology, it is widely accepted that the nanoscale phase separation with the bicontinuous interpenetrating networks and the domain sizes in the range of 10–20 nm is critical for efficient exciton diffusion and dissociation . It is worth noting that such ideal morphology actually results from the joint effects of various factors, including the natural properties of the semiconductors (solubility, crystallinity, miscibility, etc.…”

Vibrational exciton nanoimaging of phases and domains in porphyrin nanocrystals

“…This nanoscale-and molecular-level insight into the presence of disordered and ordered phases and vibrational excitons confined to few-nanometer domains can provide critical understanding for the design of functional materials. Both crystalline and amorphous phases may occur in devices made with porphyrins or other molecular materials, and tradeoffs exist between benefits of crystalline phases with typically higher charge carrier mobility and exciton diffusion length versus amorphous phases that may exhibit improved interfacial miscibility and improved charge separation (48)(49)(50)(51). The spatial organization of domains remains poorly understood across multiple length scales and is often only characterized by ensemble-averaged measurements due to the combined challenge of short length scales and low-energy scales of interaction.…”

A Biomimetic Supramolecular Approach for Charge Transfer between Donor and Acceptor Chromophores with Aggregation‐Induced Emission

“…Nevertheless, the efficiency of a device is also affected by many other factors, such as device defects, and a theoretical efficiency (23 %) has not been achieved . Optimization of these factors and the morphology of the active layer in particular to improve the overall device efficiency has received the most extensive attention in recent years . The efforts have led to the achievement of bench‐mark efficiencies above 13.1 % .…”

“…[5] Optimization of these factors and the morphology of the active layer in particulart oi mprovet he overall device efficiency has received the most extensive attention in recent years. [6] The efforts have led to the achievemento fb ench-mark efficiencies above 13.1 %. [7] The creationo ft he nanostructures has been largely achieved through tuning the solvent properties (e.g.,u sing mixtures of solvents) and using additives; [4,6] however, many of the solvents and additives are toxic.…”

“…[6] The efforts have led to the achievemento fb ench-mark efficiencies above 13.1 %. [7] The creationo ft he nanostructures has been largely achieved through tuning the solvent properties (e.g.,u sing mixtures of solvents) and using additives; [4,6] however, many of the solvents and additives are toxic. Supramolecular gels consistingo fn anofibrousn etworks have receiveds ignificant interest for organic electronics applications.T he advantages of gels include the use of greener solvents such as alcohols, and a great flexibility in tuning the nanofibrous structure.…”