Organic solar cells based on nonfullerene acceptors have recently witnessed a significant rise in their power conversion efficiency values. However, they still suffer from severe instability issues, especially in an inverted device architecture based on the zinc oxide bottom electron transport layers. In this work, we insert a pyrene-bodipy donor–acceptor dye as a thin interlayer at the photoactive layer/zinc oxide interface to suppress the degradation reaction of the nonfullerene acceptor caused by the photocatalytic activity of zinc oxide. In particular, the pyrene-bodipy-based interlayer inhibits the direct contact between the nonfullerene acceptor and zinc oxide hence preventing the decomposition of the former by zinc oxide under illumination with UV light. As a result, the device photostability was significantly improved. The π–π interaction between the nonfullerene acceptor and the bodipy part of the interlayer facilitates charge transfer from the nonfullerene acceptor toward pyrene, which is followed by intramolecular charge transfer to bodipy part and then to zinc oxide. The bodipy-pyrene modified zinc oxide also increased the degree of crystallization of the photoactive blend and the face-on stacking of the polymer donor molecules within the blend hence contributing to both enhanced charge transport and increased absorption of the incident light. Furthermore, it decreased the surface work function as well as surface energy of the zinc oxide film all impacting in improved power conversion efficiency values of the fabricated cells with champion devices reaching values up to 9.86 and 11.80% for the fullerene and nonfullerene-based devices, respectively.

Photovoltaic devices based on organic semiconductors and organo-metal halide perovskites have not yet reached the theoretically predicted power conversion efficiencies while they still exhibit poor environmental stability. Interfacial engineering using suitable materials has been recognized as an attractive approach to tackle the above issues. We introduce here a zinc porphyrin–triazine–bodipy donor−π bridge–acceptor dye as a universal electron transfer mediator in both organic and perovskite solar cells. Thanks to its “push–pull” character, this dye enhances electron transfer from the absorber layer toward the electron-selective contact, thus improving the device’s photocurrent and efficiency. The direct result is more than 10% average power conversion efficiency enhancement in both fullerene-based (from 8.65 to 9.80%) and non-fullerene-based (from 7.71 to 8.73%) organic solar cells as well as in perovskite ones (from 14.56 to 15.67%), proving the universality of our approach. Concurrently, by forming a hydrophobic network on the surface of metal oxide substrates, it improves the nanomorphology of the photoactive overlayer and contributes to efficiency stabilization. The fabricated devices of both kinds preserved more than 85% of their efficiency upon exposure to ambient conditions for more than 600 h without any encapsulation.

The presence of defects formed during the growth and crystallization of perovskite films is a limiting factor to achieve high efficiency and stability in perovskite solar cells.

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Solar cells based on metal halide perovskite and polymer donor:nonfullerene acceptor blend absorbers have recently witnessed a significant rise in their photovoltaic performance. However, they still suffer from some instability issues originating from the inferior interface quality and poor nanomorphology of the absorber layer. In this work, a series of functionalized boron‐dipyrromethene, BODIPY, molecules are introduced as ultrathin interlayers at the absorber/electron transport layer interface. This study indicates that BODIPY compounds with a high molecular dipole moment can enhance the device performance mainly due to better interface energy level alignment. They also induce passivation of defect traps and improvement in the charge transport properties of the absorber layer coated on top of them. Among the various compounds used, amino‐functionalized BODIPY, owing to the synergetic effect of the abovementioned factors, enables the highest power conversion efficiency in organic (15.69%) as well as in perovskite solar cells (20.12%). Amino‐functionalized BODIPY also demonstrates an enhanced stability under continuous illumination (in nitrogen) without and with heating (at 65 °C) for 1000 h. These results pave the way for the implementation of molecules with tailor‐made functionalities in high efficiency and stable solution‐based photovoltaic devices of the future.

Halide perovskites are a compelling candidate for the next generation of clean-energy-harvesting photovoltaic technologies owing to an unprecedented increase in power conversion efficiency, their low cost, facile fabrication and outstanding...

The design and development of novel materials with superior charge transport capabilities plays an essential role for advancing the performance of electronic devices. Ternary and doped oxides can be potentially explored because of their tailored electronic energy levels, exceptional physical properties, high electrical conductivity, excellent robustness and enhanced chemical stability. Here, a route for improving metal oxide characteristics is proposed by engineering a novel ternary oxide, namely, carbon-doped tantalum dioxyfluoride (TaO2FCx) through a straightforward synthetic route and exploring its effectiveness as an electron transport material in optoelectronic devices based on organic semiconductors. We fabricated fluorescent green organic light emitting diodes with current efficiencies of 16.53 cd/A and single-junction non-fullerene organic solar cells reaching power conversion efficiencies of 14.14 % when using the novel oxide as electron transport material outperforming the devices with the commonly used ones (such as zinc oxide). Our devices also exhibited the additional advantage of high operational and temporal stability. Non-fullerene OSCs based on the novel compound show unprecedented stability when exposed to UV light in air due to the non-defective nature of TaO2FCx. We employed a tank of experiments combined with theoretical calculations to unravel the performance merits of this novel compound. This study reveals that properly engineered ternary oxides and in particular TaO2FCx or analogous materials can enable efficient electron transport in organic optoelectronics and it is proposed as an attractive route for the broader field of optoelectronic devices including halide organic-inorganic perovskite, colloidal quantum dot and Si optoelectronics.

Organic and perovskite solar cells have recently emerged as promising candidates for next-generation solar energy technologies due to their low-cost solution-based fabrication over large areas even on flexible substrates, while offering the possibility of on-chip integration and patterning for custom-designed applications. A key concern over these emerging technologies is their poor operational stability. In a typical device architecture, the organic or perovskite absorber is usually inserted between an electron and a hole transport (extraction) layer in order to match the energetic differences present at the heterointerfaces with the respective contacts. As these layers considerably influence the device performance and operational stability, they have witnessed intense research efforts in recent years resulting in the development of novel materials. Conductive or insulating polymers, non-polymer molecular materials and transition metal oxides are among the most studied classes of interfacial materials. In this review article, we focus on the application of molecular materials, but excluding polymers, either organic or inorganic, to engineer the interfaces in these devices due to their ease of synthesis and facile functionalization of their structure to meet the requirements for successful device modification. We also include ionic compounds of well-defined stoichiometry such as CuSCN, ionic liquids and compounds of molecular anions as the polyoxometalates. We provide a comprehensive account of various molecular interlayers for organic and perovskite solar cell devices. We highlight the origin of enhanced performance and device lifetime and provide a detailed outlook for a focused future development of these materials.