wangzhaowei

An organic solar cell (OSCs) containing double bulk heterojunction (BHJ) layers, namely, double-BHJ OSCs is constructed via stamp transferring of low bandgap BHJ atop of mediate bandgap active layers. Such devices allow a large gain in photocurrent to be obtained due to enhanced photoharvest, without suffering much from the fill factor drop usually seen in thick-layer-based devices. Overall, double-BHJ OSC with optimal ≈50 nm near-infrared PDPP3T:PC₇₁BM layer atop of ≈200 nm PTB7-Th:PC₇₁BM BHJ results in high power conversion efficiencies over 12%.

An organic solar cell (OSCs) containing double bulk heterojunction (BHJ) layers, namely, double-BHJ OSCs is constructed via stamp-transferring of low bandgap BHJ layer atop of mediate bandgap active layers. Such devices obtain a large gain in photocurrent due to the enhanced photo harvest with little fill-factor drop. Overall, double-BHJ OSC results in high power conversion efficiencies over 12%.

The highest efficiencies reported for perovskite solar cells so far have been obtained mainly with methylammonium and formamidinium mixed cations. Currently, high-quality mixed-cation perovskite thin films are normally made by use of antisolvent protocols. However, the widely used “antisolvent”-assisted fabrication route suffers from challenges such as poor device reproducibility, toxic and hazardous organic solvent, and incompatibility with scalable fabrication process. Here, a simple dual-source precursor approach is developed to fabricate high-quality and mirror-like mixed-cation perovskite thin films without involving additional antisolvent process. By integrating the perovskite films into the planar heterojunction solar cells, a power conversion efficiency of 20.15% is achieved with negligible current density–voltage hysteresis. A stabilized power output approaching 20% is obtained at the maximum power point. These results shed light on fabricating highly efficient perovskite solar cells via a simple process, and pave the way for solar cell fabrication via scalable methods in the near future.

A dual-source precursor approach is developed to fabricate a high-quality and mirror-like mixed-cation perovskite without involving additional antisolvent process. By integrating the perovskite films into the planar heterojunction solar cells, a power conversion efficiency of 20.15% is achieved with negligible hysteresis effect. A stabilized power output approaching 20% is obtained at the maximum power point.

Energy barriers between the metal Fermi energy and the molecular levels of organic semiconductor devoted to charge transport play a fundamental role in the performance of organic electronic devices. Typically, techniques such as electron photoemission spectroscopy, Kelvin probe measurements, and in-device hot-electron spectroscopy have been applied to study these interfacial energy barriers. However, so far there has not been any direct method available for the determination of energy barriers at metal interfaces with n-type polymeric semiconductors. This study measures and compares metal/solution-processed electron-transporting polymer interface energy barriers by in-device hot-electron spectroscopy and ultraviolet photoemission spectroscopy. It not only demonstrates in-device hot-electron spectroscopy as a direct and reliable technique for these studies but also brings it closer to technological applications by working ex situ under ambient conditions. Moreover, this study determines that the contamination layer coming from air exposure does not play any significant role on the energy barrier alignment for charge transport. The theoretical model developed for this work confirms all the experimental observations.

In-device hot-electron spectroscopy is demonstrated as a direct and reliable technique for the determination of the energy barrier between a metal and a solution-processed electron-transporting organic semiconductor. With experimental advance, this work opens new possibilities to bring this technique closer to the organic electronics industry.

Hybrid and all-inorganic perovskite (PK) materials are a promising next generation of semiconducting materials due to their outstanding light-harvesting features, as well as their color-tunablility and efficient luminescent properties that lead to highly efficient photovoltaic and lighting devices. Bulk PK films are both ionic and electronic conductors under the presence of an externally applied electric field. In this work, the internal ion motion behavior is demonstrated within PK nanoparticles in thin-film devices by means of different long-time poling scheme assays and both static and dynamic electrochemical impedance spectroscopy measurements. In particular, the existence of a dynamic device behavior is related to the migration and rearrangement of different ionic species upon applying different driving schemes. The latter resembles the well-known signatures of the ionic motion in light-emitting electrochemical cells (LECs), that is, (i) the formation of electrical double layers due to the ionic distribution at the electrodes' interfaces, (ii) the growth of the doped regions once the charge injection is effective, and (iii) the subsequent formation of a non-doped region in the bulk of the device. Hence, this comprehensive study opens up an alternative route toward understanding the dynamics inside hybrid perovskite materials based on the large body of knowledge of LECs.

The effect of the ion motion on the mechanism of hybrid perovskite nanoparticles (PK NP) devices is investigated by static and dynamic electrochemical impedance spectroscopy and different poling schemes. Overall, these studies suggest that the electrical behavior of the PK NP devices resemble that of light-emitting electrochemical cells.

Colloidal-quantum-dot (CQD) photovoltaic devices are promising candidates for low-cost power sources owing to their low-temperature solution processability and bandgap tunability. A power conversion efficiency (PCE) of >10% is achieved for these devices; however, there are several remaining obstacles to their commercialization, including their high energy loss due to surface trap states and the complexity of the multiple-step CQD-layer-deposition process. Herein, high-efficiency photovoltaic devices prepared with CQD-ink using a phase-transfer-exchange (PTE) method are reported. Using CQD-ink, the fabrication of active layers by single-step coating and the suppression of surface trap states are achieved simultaneously. The CQD-ink photovoltaic devices achieve much higher PCEs (10.15% with a certified PCE of 9.61%) than the control devices (7.85%) owing to improved charge drift and diffusion. Notably, the CQD-ink devices show much lower energy loss than other reported high-efficiency CQD devices. This result reveals that the PTE method is an effective strategy for controlling trap states in CQDs.

A colloidal quantum dot (CQD)-ink is developed by phase-transfer exchange, enabling the fabrication of active layers by single-step coating to achieve a thick film. The CQD-ink exhibits low surface traps due to improvement of surface passivation. Thus, incorporating the CQD-ink into devices shows high efficiency and low voltage loss.

Organic–inorganic hybrid perovskite materials with mixed cations have demonstrated tremendous advances in photovoltaics recently, by showing a significant enhancement of power conversion efficiency and improved perovskite stability. Inspired by this development, this study presents the facile synthesis of mixed-cation perovskite nanocrystals based on FA_(1−x)Cs_xPbBr₃ (FA = CH(NH₂)₂). By detailed characterization of their morphological, optical, and physicochemical properties, it is found that the emission property of the perovskite, FA_(1−x)Cs_xPbBr₃, is significantly dependent on the substitution content of the Cs cations in the perovskite composition. These mixed-cation perovskites are employed as light emitters in light-emitting diodes (LEDs). With an optimized composition of FA_0.8Cs_0.2PbBr₃, the LEDs exhibit encouraging performance with a highest reported luminance of 55 005 cd m⁻² and a current efficiency of 10.09 cd A⁻¹. This work provides important instructions on the future compositional optimization of mixed-cation perovskite for obtaining high-performance LEDs. The authors believe this work is a new milestone in the development of bright and efficient perovskite LEDs.

Organic–inorganic hybrid perovskite nanocrystals with mixed cations demonstrate tremendous advances in light-emitting diodes. The physicochemical properties of synthesized perovskite nanocrystals are significantly dependent on the substitution content of the caesium cations in the perovskite composition. This work provides important instructions on the future compositional optimization of mixed-cation perovskite for obtaining high-performance light-emitting diodes.

The challenge of continuous printing in high-efficiency large-area organic solar cells is a key limiting factor for their widespread adoption. A materials design concept for achieving large-area, solution-coated all-polymer bulk heterojunction solar cells with stable phase separation morphology between the donor and acceptor is presented. The key concept lies in inhibiting strong crystallization of donor and acceptor polymers, thus forming intermixed, low crystallinity, and mostly amorphous blends. Based on experiments using donors and acceptors with different degree of crystallinity, the results show that microphase separated donor and acceptor domain sizes are inversely proportional to the crystallinity of the conjugated polymers. This methodology of using low crystallinity donors and acceptors has the added benefit of forming a consistent and robust morphology that is insensitive to different processing conditions, allowing one to easily scale up the printing process from a small-scale solution shearing coater to a large-scale continuous roll-to-roll (R2R) printer. Large-area all-polymer solar cells are continuously roll-to-roll slot die printed with power conversion efficiencies of 5%, with combined cell area up to 10 cm². This is among the highest efficiencies realized with R2R-coated active layer organic materials on flexible substrate.

The morphology formation of different all-polymer solar cells during the coating process is investigated and that a low crystalline donor and acceptor polymer blend has stable morphology between the various coating methods is identified. Large-area all-polymer solar cells are continuously roll-to-roll slot die printed with power conversion efficiencies of 5%, with combined cell area up to 10 cm².

π-Conjugated polymers are an important class of materials for organic electronics. In the past decade, numerous polymers with donor–acceptor molecular structures have been developed and used as the active materials for organic devices, such as organic field-effect transistors (OFETs) and organic photovoltaics (OPVs). The choice of the building unit is the primary step for designing the polymers. Benzochalcogenadiazoles (BXzs) are one of the most familiar acceptor building units studied in this area. As their doubly fused system, naphthobischalcogenadiazoles (NXzs), i.e., naphthobisthiadiazole (NTz), naphthobisoxadiazole (NOz), and naphthobisselenadiazole (NSz) are emerging building units that provide interesting electronic properties and highly self-assembling nature for π-conjugated polymers. With these fruitful features, π-conjugated polymers based on these building units demonstrate great performances in OFETs and OPVs. In particular, in OPVs, NTz-based polymers have exhibited more than 10% efficiency, which is among the highest values reported so far. In this Progress Report, the synthesis, properties, and structures of NXzs and their polymers is summarized. The device performance is also highlighted and the structure–property relationships of the polymers are discussed.

π-Conjugated polymers are an important class of materials for organic electronics. This recent advances of emerging π-conjugated polymers incorporating naphthobischalcogenadiazoles such as naphthobisoxadiazole, naphthobisthiadiazole, and naphthobisselenadiazle as strong acceptor building units are reviewed. The molecular design, synthesis, electronic properties, ordering structures, and device applications of these polymers are also discussed.

To improve the efficiency of existing perovskite solar cells (PSCs), a detailed understanding of the underlying device physics during their operation is essential. Here, a device model has been developed and validated that describes the operation of PSCs and quantitatively explains the role of contacts, the electron and hole transport layers, charge generation, drift and diffusion of charge carriers and recombination. The simulation to the experimental data of vacuum-deposited CH₃NH₃PbI₃ solar cells over multiple thicknesses has been fit and the device behavior under different operating conditions has been studied to delineate the influence of the external bias, charge-carrier mobilities, energetic barriers for charge injection/extraction and, different recombination channels on the solar cell performance. By doing so, a unique set of material parameters and physical processes that describe these solar cells is identified. Trap-assisted recombination at material interfaces is the dominant recombination channel limiting device performance and passivation of traps increases the power conversion efficiency (PCE) of these devices by 40%. Finally, guidelines to increase their performance have been issued and it is shown that a PCE beyond 25% is within reach.

A numerical model is developed and validated that describes the operation of perovskite solar cells and quantitatively explains the role of contacts, the charge transport layers, charge generation, drift and diffusion of carriers and recombination. By doing so, a unique set of material parameters and physical processes is identified that describes these solar cells. To increase their performance, some guidelines are issued.

Hole transport matertial (HTM) as charge selective layer in perovskite solar cells (PSCs) plays an important role in achieving high power conversion efficiency (PCE). It is known that the dopants and additives are necessary in the HTM in order to improve the hole conductivity of the HTM as well as to obtain high efficiency in PSCs, but the additives can potentially induce device instability and poor device reproducibility. In this work a new strategy to design dopant-free HTMs has been presented by modifying the HTM to include charged moieties which are accompanied with counter ions. The device based on this ionic HTM X44 dos not need any additional doping and the device shows an impressive PCE of 16.2%. Detailed characterization suggests that the incorporated counter ions in X44 can significantly affect the hole conductivity and the homogeneity of the formed HTM thin film. The superior photovoltaic performance for X44 is attributed to both efficient hole transport and effective interfacial hole transfer in the solar cell device. This work provides important insights as regards the future design of new and efficient dopant free HTMs for photovotaics or other optoelectronic applications.

A new strategy to design dopant-free hole transport materials (HTMs) by modifying the organic molecule to include charged moieties that are accompanied by counter ions is investigated. The introduced counter ions are highly beneficial for improving the conductivity of the HTM and the perovskite solar cell devices based on the designed ionic HTM show impressive power conversion efficiency of more than 16%.

Mixed ion perovskite solar cells (PSC) are manufactured with a metal-free hole contact based on press-transferred single-walled carbon nanotube (SWCNT) film infiltrated with 2,2,7,-7-tetrakis(N,N-di-p-methoxyphenylamine)-9,90-spirobifluorene (Spiro-OMeTAD). By means of maximum power point tracking, their stabilities are compared with those of standard PSCs employing spin-coated Spiro-OMeTAD and a thermally evaporated Au back contact, under full 1 sun illumination, at 60 °C, and in a N₂ atmosphere. During the 140 h experiment, the solar cells with the Au electrode experience a dramatic, irreversible efficiency loss, rendering them effectively nonoperational, whereas the SWCNT-contacted devices show only a small linear efficiency loss with an extrapolated lifetime of 580 h.

A perovskite solar cell with carbon nanotube-based hole contact and drop cast 2,2,7,7-tetrakis(N,N-di-p-methoxyphenylamine)-9,90-spirobifluorene (Spiro-OMeTAD) exhibits superior stability over the standard device with spin-coated Spiro-OMeTAD and evaporated gold contact. The solar cells are subjected to a 140 h maximum power point tracking stability experiment in 1 sun illumination and 60 °C, and the carbon-based cell outperforms the gold cell clearly.