Bridging the lab-to-fab gap in non-fullerene organic solar cells via gravure printing

Abstract

Organic solar cells have reached record efficiencies with non-fullerene acceptors, yet their translation to industrial printing remains a critical bottleneck. Here we report the highest efficiency achieved for a fully roll-to-roll-compatible gravure-printed non-fullerene organic solar cell. High-performance blends are typically optimised under laboratory coating conditions, while roll-to-roll manufacturing imposes fundamentally different constraints on ink stability, drying dynamics, and multilayer integration. Whether these constraints intrinsically limit device physics has remained unresolved. Here, we demonstrate a gravure-printed PM6:Y12 solar cell architecture using commercially available materials and establish a quantitative framework that disentangles optical, recombination, and transport losses in printed devices. We find that favourable bulk morphology and exciton harvesting can be preserved under gravure printing and non-halogenated solvents. The dominant efficiency penalties arise instead from optical interference within the printed layer stack and slow charge transport. Our results demonstrate that the performance gap between laboratory and printed solar cells is originating from device architecture rather than the intrinsic physics of modern non-fullerene systems, providing a mechanistic roadmap for roll-to-roll manufacturing of non-fullerene solar cells.

Figures (26)

• Figure 1: Layer stacks and fabrication methods for (a) spin-coated reference and (b) printed PM6:Y12 OSCs. (c) Photograph of the printed solar cell. (d) Vertical thickness profiles and (e) corresponding gray scale optical micrographs of gravure-printed o-xylene-based PM6:Y12 films using ink concentrations of 16, 18 and 22 mg ml$^{-1}$ and gravure forms with 22 ml m$^{-2}$ (denoted S) and 26 ml m$^{-2}$ (denoted L) cell volume. Higher ink concentration leads to higher average film thickness and larger lateral thickness variations. For the 22 mg ml$^{-1}$ sample pronounced non-uniformity is observed, which is overcome by using larger printing form.
• Figure 2: (a) JV characteristics, and (b) EQE spectra of gravure-printed and spin-coated o-xylene-based PM6:Y12 devices. JV curves were measured under 1 sun equivalent illumination provided by Wavelabs LS2 solar simulator (for spectrum, see Figure \ref{['SI_fig:spectrum']}). (c) PCE values of R2R-compatible OSCs from literature compared to current work, highlighting different AL deposition methods (slot-die coating, inkjet printing, and gravure printing) and active-layer systems for NFA OSCs. The parameters and references are listed in Table \ref{['SI_tab:PCE_lit']}.
• Figure 3: (a) Ordinary and extraordinary absorption coefficients for spin-coated and gravure-printed PM6:Y12 films determined by VASE, revealing optical anisotropy and showing reduced absorption strength in printed films. (b-d) Optical transfer-matrix modelling of the generation current density $J_\mathrm{gen}$: (b) influence of the AL optical constants on photogeneration; (c) effect of PEDOT:PSS thickness on $J_\mathrm{gen}$; (d) comparison of different bottom electrode and ETL configurations.
• Figure 4: Various loss parameters in spin-coated and gravure-printed PM6:Y12 solar cells processed from chloroform and o-xylene. (a) Decomposition of $V_\mathrm{oc}$ losses into the Shockley--Queisser radiative limit, the additional radiative loss associated with non-ideal absorption, and the non-radiative recombination loss. (b) Analysis of $F\!F$ losses. JV characteristics are normalised to highlight differences in $F\!F$; the inset shows the extracted transport figure of merit $\beta_\mathrm{MPP}$. (c) $F\!F$ losses separated into contributions related to recombination (shaded grey), transport (shaded yellow), and external series resistance (shaded orange). The solid lines indicate the fill factors expected in the absence of the corresponding losses. (d) Charge-carrier mobilities derived from IMPS measurements.
• Figure S1: Current--voltage characteristics of printed PM6:Y12 solar cells based on thick ($\sim$128 nm) and thin ($\sim$88 nm) active layers. Even though thick active layers lead to increased $J_\mathrm{sc}$, the study focuses on thin active-layer solar cells for better comparison to spin-coated references.