Organic solvent nanofiltration (OSN) membranes with ultrathin separation layers down to 35 nm in thickness fabricated from a polymer of intrinsic microporosity (PIM‐1) are presented. These membranes exhibit exceptionally fast permeation of n‐heptane with a rejection for hexaphenylbenzene of about 90%. A 35 nm thick PIM‐1 membrane possesses a Young's modulus of 222 MPa, and shows excellent stability under hydraulic pressures of up to 15 bar in OSN. A maximum permeance for n‐heptane of 18 Lm⁻²h⁻¹bar⁻¹ is achieved with a 140 nm thick membrane, which is about two orders of magnitude higher than Starmem240 (a commercial polyimide‐based OSN membrane). Unexpectedly, decreasing the film thickness below 140 nm results in an anomalous decrease in permeance, which appears to be related to a packing enhancement of PIM‐1, as measured by light interferometry. Further, thermal annealing of the membranes formed from PIM‐1 reveals that their permeance is preserved up to temperatures in excess of 150 °C, whereas the permeance of conventional, integrally skinned, asymmetric polyimide OSN membranes decreases significantly when they are annealed under the same conditions. To rationalize this key difference in response of functional performance to annealing, the concept of membranes with intrinsic microporosity (MIMs) versus membranes with extrinsic microporosity (MEMs) is introduced.

This review highlights the opportunities and challenges in stability of organic solar cells arising from the emergence of non-fullerene acceptors.

A key challenge to the commercialization of organic bulk heterojunction solar cells is the achievement of morphological stability, particularly under thermal stress conditions. Here we show that a low-level light exposure processing step during fabrication of blend polymer:PC₆₀BM solar cells can result in a 10-fold increase in device thermal stability and, under certain conditions, enhanced device performance. The enhanced stability is linked to the light-induced oligomerization of PC₆₀BM that effectively hinders their diffusion and crystallization in the blend. We thus suggest that light processing may be a promising, general and cost-effective strategy to optimize fullerene-based solar cell performance. The low level of light exposure required suggests not only that this may be an easily implementable strategy to enhance performance, but also that light-induced PC₆₀BM oligomerization may have inadvertently influenced previous studies of organic solar cell device behaviour.

Morphological stability is a key requirement for outdoor operation of organic solar cells. We demonstrate that morphological stability and lifetime of polymer/fullerene based solar cells under thermal stress depend strongly on the substrate interface on which the active layer is deposited. In particular, we find that the stability of benchmark PCDTBT/PCBM solar cells under modest thermal stress is substantially increased in inverted solar cells employing a ZnO substrate compared to conventional devices employing a PEDOT:PSS substrate. This improved stability is observed to correlate with PCBM nucleation at the 50 nm scale, which is shown to be strongly influenced by different substrate interfaces. Employing this approach, we demonstrate remarkable thermal stability for inverted PCDTBT:PC₇₀BM devices on ZnO substrates, with negligible (<2%) loss of power conversion efficiency over 160 h under 85 °C thermal stress and minimal thermally induced “burn-in” effect. We thus conclude that inverted organic solar cells, in addition to showing improved environmental stability against ambient humidity exposure as widely reported previously, can also demonstrate enhanced morphological stability. As such we show that the choice of suitable substrate interfaces may be a key factor in achieving prolonged lifetimes for organic solar cells under thermal stress conditions.