Key factors behind the superior performance of polymer-based NFA blends.

All-small molecule (ASMs) solar cells have great potential to actualize the commercialization of organic photovoltaics owing to their higher solubility, lesser batch-to-batch variety and simpler synthesis routes compared to the blend systems that utilize conjugated polymers. However, the efficiencies of the ASMs are slightly lacking behind the polymer: small molecule bulk-heterojunctions. To address this discrepancy, we compare an ASM blend ZR1:Y6 with a polymer:small molecule blend PM7:Y6, sharing the same non-fullerene acceptor (NFA). Our analyses reveal similar energetic offset between the exciton singlet state and charge transfer state (ΔES1-CT) in ZR1:Y6 and PM7:Y6. In comparison to the latter, surprisingly, the ZR1:Y6 has noticeably a stronger field-dependency of charge generation. Low charge carrier mobilities of ZR1:Y6 measured, using space charge limited current measurements, entail a viable explanation for suppressed charge dissociation. Less crystalline and more intermixed domains as observed in the ZR1:Y6 system compared to polymer:Y6 blends, makes it difficult for NFA to form a continuous pathway for electron transport, which reduces the charge carrier mobility.

Resolving electron and hole transport properties in semiconductor materials by constant light-induced magneto transport.

The knowledge of minority and majority charge carrier properties enables controlling the performance of solar cells, transistors, detectors, sensors, and LEDs. Here, we developed the constant light induced magneto transport method which resolves electron and hole mobility, lifetime, diffusion coefficient and length, and quasi-Fermi level splitting. We demonstrate the implication of the constant light induced magneto transport for silicon and metal halide perovskite films. We resolve the transport properties of electrons and holes predicting the material's effectiveness for solar cell application without making the full device. The accessibility of fourteen material parameters paves the way for in-depth exploration of causal mechanisms limiting the efficiency and functionality of material structures. To demonstrate broad applicability, we further characterized twelve materials with drift mobilities spanning from 10-3 to 103 cm2V-1s-1 and lifetimes varying between 10-9 and 10-3 seconds. The universality of our method its potential to advance optoelectronic devices in various technological fields.

What is special about Y6; the working mechanism of neat Y6 organic solar cells.

Non-fullerene acceptors (NFAs) have delivered advancement in bulk heterojunction organic solar cell efficiencies, with a significant milestone of 20% now in sight. However, these materials challenge the accepted wisdom of how organic solar cells work. In this work we present a neat Y6 device with an efficiency above 4.5%. We thoroughly investigate mechanisms of charge generation and recombination as well as transport in order to understand what is special about Y6. Our data suggest that Y6 generates bulk free charges, with ambipolar mobility, which can be extracted in the presence of transport layers.

Overcoming C60-induced interfacial recombination in inverted perovskite solar cells by electron-transporting carborane.

Inverted perovskite solar cells still suffer from significant non-radiative recombination losses at the perovskite surface and across the perovskite/C60 interface, limiting the future development of perovskite-based single- and multi-junction photovoltaics. Therefore, more effective inter- or transport layers are urgently required. To tackle these recombination losses, we introduce ortho-carborane as an interlayer material that has a spherical molecular structure and a three-dimensional aromaticity. Based on a variety of experimental techniques, we show that ortho-carborane decorated with phenylamino groups effectively passivates the perovskite surface and essentially eliminates the non-radiative recombination loss across the perovskite/C60 interface with high thermal stability. We further demonstrate the potential of carborane as an electron transport material, facilitating electron extraction while blocking holes from the interface. The resulting inverted perovskite solar cells deliver a power conversion efficiency of over 23% with a low non-radiative voltage loss of 110 mV, and retain >97% of the initial efficiency after 400 h of maximum power point tracking. Overall, the designed carborane based interlayer simultaneously enables passivation, electron-transport and hole-blocking and paves the way toward more efficient and stable perovskite solar cells.