Morphological Engineering of Organic Photovoltaic Thin Films

Organic photovoltaic devices rely on finely tuned microstructures within the photoactive thin film to maximise exciton dissociation and charge transport. Morphological engineering encompasses the deliberate control of phase separation, domain purity, crystallinity and vertical composition gradients through solvent selection, processing additives, thermal or solvent annealing and controlled drying kinetics. Advances in in situ characterisation and computational modelling have elucidated the dynamic evolution of polymer–acceptor mixtures, enabling predictive control over nano- and microscale architectures. The resulting optimisation of interpenetrating networks and percolating pathways has led to significant improvements in power conversion efficiency, operational stability and manufacturability of low-cost, flexible solar modules.

Research from Nature Portfolio

Recent studies have constructed detailed phase diagrams for blends of the donor polymer PTB7-Th with the non-fullerene acceptor ITIC using Flory–Huggins lattice theory. These investigations revealed critical composition thresholds at approximately 60–70 wt.% acceptor, corresponding to a sharp transition in surface polarity and the onset of ITIC crystallite formation. Atomic force microscopy and X-ray diffraction were used to correlate blend composition with domain architecture, providing robust design rules for tuning morphology–performance relationships in emerging non-fullerene organic solar cells.

Morphological Engineering of Organic Photovoltaic Thin Films publication trend

The graph below shows the total number of articles in morphological engineering of organic photovoltaic thin films across all publications each year (not limited to Nature Index journals).

Technical terms

Bulk heterojunction: an interpenetrating network of electron-donor and acceptor materials that facilitates exciton dissociation and charge transport.

Flory–Huggins interaction parameter: a dimensionless thermodynamic constant quantifying the enthalpic interaction between polymer and solvent or between polymer components, governing their miscibility.

Spinodal decomposition: a spontaneous phase-separation mechanism in an unstable mixture that produces interconnected domains without a nucleation barrier.

Phase-field simulation: a computational technique that describes microstructure evolution by coupling spatially continuous order parameters to thermodynamic potentials and kinetic laws.

Grazing incidence small-angle X-ray scattering (GISAXS): an in situ characterisation method that probes nanoscale film morphology by detecting X-ray scattering at low incident angles.

References

1. Phase behavior of π-conjugated polymer and non-fullerene acceptor (PTB7-Th:ITIC) solutions and blends. Scientific Reports (2022).
2. Sub‐Micrometer Structure Formation during Spin Coating Revealed by Time‐Resolved In Situ Laser and X‐Ray Scattering. Advanced Functional Materials (2017).
3. Phase Diagrams of Ternary π-Conjugated Polymer Solutions for Organic Photovoltaics. Polymers (2021).
4. Crystalline morphology formation in phase-field simulations of binary mixtures. Journal of Materials Chemistry C (2023).
5. A mesoscopic lattice model for morphology formation in ternary mixtures with evaporation. Communications in Nonlinear Science and Numerical Simulation (2023).