Optoelectronic Design of Organic Solar Cells

Organic solar cells harness conjugated polymers and small molecules to convert sunlight into electricity via tunable optoelectronic processes. The design of these devices centres on controlling light absorption, exciton generation and separation, and charge transport within a nanoscale active layer. Photovoltaic performance is largely determined by the alignment of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of donor and acceptor components, the morphology of bulk heterojunction blends, and the kinetics of exciton dissociation at donor–acceptor interfaces. Recent advances have focused on non-fullerene acceptor architectures, molecular engineering of donor polymers, and precise interface modification to achieve broader absorption spectra, reduced recombination losses and enhanced charge-carrier mobilities. Computation-guided design, coupled with refined synthetic routes, is rapidly expanding the library of chromophores with optimised band gaps and favourable energetics, driving improvements in power conversion efficiencies while maintaining lightweight, flexible and low-cost fabrication techniques. Ongoing efforts address stability under oxygen and moisture, device lifetime and large-area scalability to pave the way for commercial impact and integration into portable and building-integrated photovoltaics.

Research from Nature Portfolio

Recent studies have developed peripheral symmetric acceptors built on a tetrathienylbenzene core, achieving notable reductions in energy gaps and stronger bathochromic shifts in the visible spectrum by tailoring end-capped electron-withdrawing moieties. This class of chromophores exhibited broader absorption up to 606 nm in solvent media and lower exciton binding energies, indicating more efficient charge separation. Complementary work on benzothiophene-incorporated non-fullerene acceptors demonstrated that fusing rigid ring systems to dithiophene backbones narrows band gaps to below 1.6 eV and extends absorption into the near-infrared region, while lowering reorganisation energies for both electrons and holes. Another strand of research has introduced difluorobenzene and quinoline cores into non-fullerene acceptors, where density functional theory predicted favourable frontier orbital energies, λmax values beyond 600 nm and open-circuit voltages above 1 V, showcasing these materials as promising candidates for bulk heterojunction architectures.

Optoelectronic Design of Organic Solar Cells publication trend

The graph below shows the total number of articles in optoelectronic design of organic solar cells across all publications each year (not limited to Nature Index journals).

Technical terms

Bulk heterojunction (BHJ): A phase-separated blend of donor and acceptor materials forming interpenetrating networks for efficient exciton dissociation.

Non-fullerene acceptor (NFA): A class of electron-accepting small molecules or polymers that serve as alternatives to fullerene derivatives in organic solar cells.

Frontier molecular orbitals (HOMO/LUMO): The highest occupied and lowest unoccupied orbitals that determine a molecule’s ionisation energy, electron affinity and optical gap.

Reorganisation energy: The energy required to reorganise molecular geometry during charge transfer, inversely related to carrier mobility.

Exciton binding energy: The energy needed to separate a bound electron–hole pair (exciton) into free charge carriers.

Open-circuit voltage (Voc): The maximum voltage a solar cell can deliver when no current is drawn, influenced by donor and acceptor energy level offsets.

References

1. Unveiling peripheral symmetric acceptors coupling with tetrathienylbenzene core to promote electron transfer dynamics in organic photovoltaics. Scientific Reports (2024).
2. First theoretical framework for highly efficient photovoltaic parameters by structural modification with benzothiophene-incorporated acceptors in dithiophene based chromophores. Scientific Reports (2022).
3. Designing small organic non-fullerene acceptor molecules with diflorobenzene or quinoline core and dithiophene donor moiety through density functional theory. Scientific Reports (2021).
4. Designing Electron-Deficient Diketone Unit Based Non-Fused Ring Acceptors with Amplified Optoelectronic Features for Highly Efficient Organic Solar Cells: A DFT Study. Molecules (2023).
5. Effect of Benzothiadiazole-Based π‑Spacers on Fine-Tuning of Optoelectronic Properties of Oligothiophene-Core Donor Materials for Efficient Organic Solar Cells: A DFT Study. The Journal of Physical Chemistry A (2023).
6. Impact of various heterocyclic π-linkers and their substitution position on the opto-electronic attributes of the A–π–D–π–A type IECIO-4F molecule: a comparative analysis. RSC Advances (2022).