The HOPES project was organized around five work packages targeting the development of high-efficiency indoor OPVs through high-throughput experimentation combined with a tunable light source. The following summarizes the key technical and scientific activities carried out and their outcomes.
WP1—Training and Development: The researcher underwent comprehensive training at the NANOPTO group (ICMAB-CSIC) on high-throughput fabrication and characterization tools, including blade coating, four-point probe, EQE, SOLS, and advanced statistical analysis. A career development plan was established in consultation with the supervisor, Prof. Mariano Campoy-Quiles, and regularly reviewed throughout the fellowship.
WP2—Tuning the Light Spectrum: A computer-controlled spectrum-on-demand light source (SOLS) was successfully implemented and calibrated. The SOLS system, patented by the host group, delivers tunable spectra across 380–1100 nm with excellent temporal stability (<2%) and spatial homogeneity (<5%), fully compliant with IEC-recommended indoor characterization standards. After screening several, four distinct indoor LED spectra were selected and generated (2700 K, 5200 K, 6500 K, and B4), enabling systematic evaluation of OPV devices under realistic and varied indoor illumination conditions. This fulfilled RO1.
WP3—Absolute Maximum Efficiency for a Model Material System: A high-throughput blade-coating methodology was implemented to fabricate continuous active-layer thickness gradients (50–450 nm) on large-aspect-ratio ITO substrates, each hosting 24 individual devices. Five binary donor:acceptor blends were investigated: PTQ10:o-IDFBR, PTQ10:eh-IDTBR, PM6:FCC-Cl, PTQ10:FCC-Cl, and D18:FCC-Cl. Devices were fabricated in an inverted architecture (glass/ITO/ZnO/active layer/MoO₃/Ag) and characterized under both 1-sun and four indoor LED spectra with varied light intensity, yielding a total of over 2400 device measurements. Under 1-sun illumination, PTQ10:FCC-Cl achieved the highest PCE of 10.2% with a stable fill factor (~70%), while PM6:FCC-Cl reached 9.39%. Under indoor 2700 K LED illumination, PM6:FCC-Cl attained a peak PCE of 26.4% at ~344 nm—to the best of our knowledge, the highest reported PCE for blade-coated indoor OPVs—while PTQ10:FCC-Cl achieved 21.7% at ~355 nm. This fulfilled RO2.
WP4—Materials Screening: Systematic thickness- and spectrum-dependent performance analysis across five material systems revealed key design principles for indoor OPVs. PTQ10:FCC-Cl demonstrated the broadest thickness tolerance (≈230–410 nm) and strong spectral robustness, with PCE varying by only ≈2.6% across all four indoor spectra. In contrast, PM6:FCC-Cl showed higher peak PCE but pronounced thickness sensitivity, with optimal performance confined to a narrow range (~305 nm) and PCE varying by ≈15% across spectra. Shunt resistance (RP) analysis showed that intermediate thicknesses maximize RP and fill factor, while very thin layers suffer leakage and very thick layers develop recombination pathways. Transfer matrix modeling (TMM) validated experimental JSC trends, and GIWAXS analysis confirmed that crystalline order and paracrystalline disorder parameters vary with thickness, with PM6:FCC-Cl showing the most thickness-sensitive microstructure. AFM morphology characterization further confirmed that PTQ10-based blends maintain smoother, more uniform surfaces across a broad thickness range, consistent with their superior thickness tolerance. Critically, the study established that light intensity has a more pronounced impact on indoor OPV performance than spectral distribution, providing a key design rule for material selection. This fulfilled RO3.
WP5—Secondment at Epishine (Sweden): The researcher completed a secondment at Epishine AB, a leading European company in indoor OPV technology, where activities focused on upscaling the best-performing device architectures identified in WP4 toward a functional prototype, targeting integration with IoT devices (RO4).
