Non-fullerene acceptor organic photovoltaics with intrinsic operational lifetimes over 30 years

Abstract

Organic photovoltaic cells (OPVs) have the potential of becoming a productive renewable energy technology if the requirements of low cost, high efficiency and prolonged lifetime are simultaneously fulfilled. So far, the remaining unfulfilled promise of this technology is its inadequate operational lifetime. Here, we demonstrate that the instability of NFA solar cells arises primarily from chemical changes at organic/inorganic interfaces bounding the bulk heterojunction active region. Encapsulated devices stabilized by additional protective buffer layers as well as the integration of a simple solution processed ultraviolet filtering layer, maintain 94% of their initial efficiency under simulated, 1 sun intensity, AM1.5 G irradiation for 1900 hours at 55 °C. Accelerated aging is also induced by exposure of light illumination intensities up to 27 suns, and operation temperatures as high as 65 °C. An extrapolated intrinsic lifetime of > 5.6 × 10⁴ h is obtained, which is equivalent to 30 years outdoor exposure.

Fig. 1. Device structure, molecular structures, and OPV ageing data under 1 sun simulated AM1.5 G illumination.

a Schematic of the device showing layer thicknesses and compositions (right): molecular structural formulae of the PCE-10 and BT-CIC (left): molecular structural formulae of the cathode and anode buffer materials. b PCE power conversion efficiency, c V_OC Open-circuit voltage, d J_SC Short circuit current, and e FF Fill factor, plotted vs. aging time under 1 sun simulated AM1.5 G illumination for 3000 h with different device architectures (populations of 3–4 devices). The error bars indicate the 1 s.d. uncertainty of each measurement.

Fig. 2. OPV efficiency under accelerated aging conditions.

a Normalized PCE plotted vs. aging time under illumination equivalent to 10 ± 1.2, 20 ± 2.5, and 27 ± 3.8 suns. b Normalized PCE plotted vs. aging time under simulated AM1.5 G one sun illumination with temperature of 45 ± 5, 55 ± 5, and 65 ± 5 °C (populations of 3–4 devices). The error bars indicate the 1 s.d. uncertainty of PCE measurements.

Fig. 3. GIWAXS characterization and TEM images.

a In-plane (dotted line) and out-of-plane (solid line) sector-averaged profiles extracted from grazing incidence wide-angle X-ray scattering (GIWAXS) patterns; q is the scattering vector. b Transmission electron microscope (TEM) image of cross-sectional slices of a fresh PCE-10:BT-CIC device without an interface buffer layer. c Fresh PCE-10:BT-CIC device with an IC-SAM layer inserted at the ZnO/BHJ interface. d Aged PCE-10:BT-CIC device with an IC-SAM layer inserted at the ZnO/BHJ interface under 27 ± 3.8 suns illumination for 870 h.

Fig. 4. Assessment of the stability of the organic/inorganic interface.

UV-Vis absorption spectra plotted vs. aging time under ultraviolet illumination with intensity equivalent to 60 suns of thin film of a PCE-10 on ZnO, b BT-CIC on ZnO, c BT-CIC on ZnO with an IC-SAM buffer, and d PCE-10:BT-CIC on ZnO with an IC-SAM buffer. X-ray photoelectron spectra of Mo 3d for the fresh device without e 2 nm C₇₀ layer, f aged device without C₇₀ layer, g fresh device with C₇₀ layer, and h aged device with C₇₀ layer. The Gaussian distributions used to fit the spectrum and the sum of these Gaussians are shown by the solid lines. The black lines, which are often buried by the summation fit (green lines), correspond to the experimental results.

Fig. 5. Characterization of the ZnO UV filter.

a UV-Vis absorption spectra of a ZnO UV filter plotted vs. aging time under simulated AM1.5 G 1 sun illumination in air over 65 days. b Current-density-voltage characteristics, and c external quantum efficiency (EQE) spectra of fresh PCE-10:BT-CIC (1:1.5, w/w) devices with a ZnO UV filter, as well as the aged device under simulated AM1.5 G 1 sun illumination. d Normalized PCE plotted vs. aging time under ultraviolet illumination equivalent to 60 suns for more than 350 h with and without ZnO UV filter. The error bars indicate the 1 s.d. uncertainty of PCE measurements.

Fig. 6. Aging acceleration factor and extrapolated OPV lifetime.

Normalized PCE plotted vs. the equivalent 1 sun exposure time, defined as time (h) multiplied by intensity (suns) raised to the power of 2.02, for OPV cells under all illumination conditions used in this work. The data are fit to an exponential to estimate the time for the PCE to drop to 80% of its initial value, T₈₀, with the best fit shown as a solid line. The error bar indicates the 1 s.d. uncertainty of the PCE measurements.