The application of liquid‐exfoliated 2D transition metal disulfides (TMDs) as the hole transport layers (HTLs) in nonfullerene‐based organic solar cells is reported. It is shown that solution processing of few‐layer WS2 or MoS2 suspensions directly onto transparent indium tin oxide (ITO) electrodes changes their work function without the need for any further treatment. HTLs comprising WS2 are found to exhibit higher uniformity on ITO than those of MoS2 and consistently yield solar cells with superior power conversion efficiency (PCE), improved fill factor (FF), enhanced short‐circuit current (JSC), and lower series resistance than devices based on poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) and MoS2. Cells based on the ternary bulk‐heterojunction PBDB‐T‐2F:Y6:PC71BM with WS2 as the HTL exhibit the highest PCE of 17%, with an FF of 78%, open‐circuit voltage of 0.84 V, and a JSC of 26 mA cm−2. Analysis of the cells' optical and carrier recombination characteristics indicates that the enhanced performance is most likely attributed to a combination of favorable photonic structure and reduced bimolecular recombination losses in WS2‐based cells. The achieved PCE is the highest reported to date for organic solar cells comprised of 2D charge transport interlayers and highlights the potential of TMDs as inexpensive HTLs for high‐efficiency organic photovoltaics.

We report on bulk-heterojunction (BHJ) organic photovoltaics (OPVs) based on the self-assembled monolayer (SAM) 2PACz as a hole-selective interlayer functionalized directly onto the indium tin oxide (ITO) anode. The 2PACz is found to change the work function of ITO while simultaneously affecting the morphology of the BHJ deposited atop. Cells with PM6:N3 BHJ and ITO-2PACz anode exhibit a power conversion efficiency (PCE) of 16.6%, which is greater than that measured for bare ITO (6.45%) and ITO/PEDOT:PSS (15.94%) based devices. The enhanced performance is attributed to lower contact-resistance, reduced bimolecular recombination losses, and improved charge transport within the BHJ. Importantly, the ITO-2PACz-based OPVs show dramatically improved operational stability when compared with PEDOT:PSS-based cells. When the ITO-2PACz anode is combined with the ternary PM6:BTP-eC9:PC 71 BM BHJ, the resulting cells exhibit a maximum PCE of 18.03%, highlighting the potential of engineered SAMs for use in hole-selective contacts in high-performance OPVs.

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High mobility thin‐film transistor technologies that can be implemented using simple and inexpensive fabrication methods are in great demand because of their applicability in a wide range of emerging optoelectronics. Here, a novel concept of thin‐film transistors is reported that exploits the enhanced electron transport properties of low‐dimensional polycrystalline heterojunctions and quasi‐superlattices (QSLs) consisting of alternating layers of In2O3, Ga2O3, and ZnO grown by sequential spin casting of different precursors in air at low temperatures (180–200 °C). Optimized prototype QSL transistors exhibit band‐like transport with electron mobilities approximately a tenfold greater (25–45 cm2 V−1 s−1) than single oxide devices (typically 2–5 cm2 V−1 s−1). Based on temperature‐dependent electron transport and capacitance‐voltage measurements, it is argued that the enhanced performance arises from the presence of quasi 2D electron gas‐like systems formed at the carefully engineered oxide heterointerfaces. The QSL transistor concept proposed here can in principle extend to a range of other oxide material systems and deposition methods (sputtering, atomic layer deposition, spray pyrolysis, roll‐to‐roll, etc.) and can be seen as an extremely promising technology for application in next‐generation large area optoelectronics such as ultrahigh definition optical displays and large‐area microelectronics where high performance is a key requirement.

Molecular doping has recently been shown to improve the operating characteristics of organic photovoltaics (OPVs). Here, we prepare neutral Diquat (DQ) and use it as n-dopant to improve the performance of state-of-the-art OPVs. Adding DQ in ternary bulk-heterojunction (BHJ) cells based of PM6:Y6:PC 71 BM is found to consistently increase their power conversion efficiency (PCE) from 16.7 to 17.4%. Analyses of materials and devices reveal that DQ acts as n-type dopant and morphology modifier for the BHJ leading to observable changes in its surface topography. The resulting n-doped BHJs exhibit higher optical absorption coefficients, balanced ambipolar transport, longer carrier lifetimes and suppressed bimolecular recombination, which are ultimately responsible for the increased PCE. The use of DQ was successfully extended to OPVs based on PM6:BTP-eC9:PC 71 BM for which a maximum PCE of 18.3% (uncertified) was achieved. Our study highlights DQ as a promising dopant for application in next generation organic solar cells.

Molecular doping is often used in organic semiconductors to tune their (opto)electronic properties. Despite its versatility, however, its application in organic photovoltaics (OPVs) remains limited and restricted to p‐type dopants. In an effort to control the charge transport within the bulk‐heterojunction (BHJ) of OPVs, the n‐type dopant benzyl viologen (BV) is incorporated in a BHJ composed of the donor polymer PM6 and the small‐molecule acceptor IT‐4F. The power conversion efficiency (PCE) of the cells is found to increase from 13.2% to 14.4% upon addition of 0.004 wt% BV. Analysis of the photoactive materials and devices reveals that BV acts simultaneously as n‐type dopant and microstructure modifier for the BHJ. Under optimal BV concentrations, these synergistic effects result in balanced hole and electron mobilities, higher absorption coefficients and increased charge‐carrier density within the BHJ, while significantly extending the cells' shelf‐lifetime. The n‐type doping strategy is applied to five additional BHJ systems, for which similarly remarkable performance improvements are obtained. OPVs of particular interest are based on the ternary PM6:Y6:PC71BM:BV(0.004 wt%) blend for which a maximum PCE of 17.1%, is obtained. The effectiveness of the n‐doping strategy highlights electron transport in NFA‐based OPVs as being a key issue.

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Engineering of solution-grown metal oxide heterointerfaces presents an alternative strategy for thin-film transistor development.