Role of Molecular Architecture in Organic Photovoltaic Cells

Abstract

What are the stumbling blocks for achieving high-efficiency organic photovoltaic devices? This question is examined from a molecular architecture and molecular packing perspective. The intermolecular interaction between the electron donor and electron acceptor influences the charge separation. The packing of electron donors and acceptors influences the charge transport. Therefore, there is a need to strike a balance between the chargetransfer interactions and packing interactions and obtain nanoscale segregated morphologies for efficient charge separation and charge transport. Molecular architecture is key toward striking this balance and, therefore, its impact on charge-transfer interactions and packing interactions; thus, the active-layer morphology and photovoltaic metrics are examined. A variety of molecular architectures for the packing of π-conjugated organic molecules to structures relevant for photovoltaic devices is also discussed.

Strategies for controlling the active layer morphologies in OPVs

“…It is now well understood that there are three factors that concurrently facilitate the formation of a BHJ in the P3HT-PCBM system. 3,49,50 These are (1) the propensity of P3HT to rapidly crystallize in the presence of PCBM, (2) the large diffusion coefficient of PCBM in amorphous P3HT and (3) the slow kinetics of crystallization of PCBM in the presence of P3HT. It is noteworthy that the HR TEM images reported by Russell and coworkers 49 also show that the interface between PEDOT/PSS and P3HT becomes stronger after the annealing process.…”

“…[3][4][5] The photons are absorbed by the conjugated polymer, which creates excited electron-hole pairs. These electronhole pairs, excitons, either recombine to emit light or heat or, in a more useful process, dissociate and move to their respective electrodes to result in a photovoltaic current.…”

Charge transport in amorphous low bandgap conjugated polymer/fullerene films

“…% PCBM, indicating that PCBM is macroscopically phase-separated upon annealing where electrons may easily be trapped in PCBM domains. 14,15 Comparison of charge mobility of an unannealed device with that of an annealed one indicates that annealing does not enhance charge mobility for amorphous conjugated polymer P(3HT-MeTDQ).…”

“…These values are dependent strongly on photophysical properties of specific D/A material and its blending morphology. [14][15][16] However, phase behavior at molecular levels, including spatial arrangement of amorphous polymeric chain/fullerene in blends, has still been far from a complete understanding due to its complex nature. In 2008, two research groups reported the binary phase diagrams of semicrystalline poly(3-hexyl thiophene) (P3HT)/ PCBM blends 17 and amorphous poly(phenylene vinylene) (PPV) derivative/PCBM.…”

Fluorene-based macromolecular nanostructures and nanomaterials for organic (opto)electronics

“…Previously, many efforts have been made to clarify low-energy green emission bands (also called g-bands) in PF-based electroluminescent thin films for application in high-performance devices [86]. Organic nanosystems from fully conjugated block copolymers offer a new solution for solar cells [87,88]. Self-assembly of p-n fully conjugated diblock copolymers can achieve nanostructured thin films with two ordered independent channels of electrons and hole.…”