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Correction for ‘Efficient non-fullerene organic solar cells employing sequentially deposited donor–acceptor layers’ by Jiangbin Zhang et al., J. Mater. Chem. A, 2018, 6, 18225–18233.

Non-fullerene acceptors (NFAs) have recently outperformed their fullerene counterparts in binary bulk-heterojunction (BHJ) organic solar cells (OSCs). Further development of NFA OSCs may benefit other novel OSC device structures that alter or extend the standard BHJ concept. Here, we report such a new processing route that forms a BHJ-like morphology between sequentially processed polymer donor and NFA with high power conversion efficiencies in excess of 10%. Both devices show similar charge generation and recombination behaviours, supporting formation of similar BHJ active layers. We correlate the ~30 meV smaller open-circuit voltage in sq-BHJ devices to more substantial non-radiative recombination by voltage loss analysis. We also determine the exciton diffusion length of benchmark polymer PBDB-T to be 10 ± 3 nm. Our results demonstrate high-efficiency OSC devices using sequential deposition method and provide new opportunities to further improve performance of state-of-the-art OSCs.

A comprehensive understanding of the charge generation mechanism in organic solar cells is critical for further improvement of device performance. Currently, the origin and magnitude of the coulombic binding energy of the charge-transfer state (CTS), an intermediate state which is fundamental for the charge separation process, are still under debate. Here, we propose a new approach for determining the dissociation energy of localised CTSs for a range of devices with different alignments of molecular energy levels (tuned by chemical modifications of fullerene) and disorder (adjusted by the blend composition) using temperature-dependent pump-push photocurrent spectroscopy. We observe that the dissociation of localised CTSs from initial excitation is a temperature-dependent process, and we determined the binding energy of these CTSs by measuring a single activation energy over a wide temperature range. We propose a simple qualitative picture to explain the observation, based on the split between the bound CTSs and free charges. In all the material systems studied here, the activation energy falls within the range of 90 ± 50 meV (corresponding to ∼1 nm separation of an electron–hole pair). Surprisingly, the binding energy does not depend on the material composition or the driving energy (∼150 meV variation) for charge separation. In contrast, the number of formed bound states and their following recombination dynamics are material- and nanomorphology-sensitive. Such observations in the studied benchmark polymer:fullerene systems reveal unexpected similarities in the energetics of CTSs formed in different electronic environments. This makes our results of general importance for understanding the photophysics at the heterojunction interface and for further development of organic photovoltaics.