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All-inorganic cesium halide perovskite materials are intensively investigated due to their excellent photoelectric characteristics, but poor film coverage, unbalanced charge carrier transporting and insufficient exciton harvesting are remaining challenges to be overcome in order to achieve high electroluminescent (EL) performance in perovskite light-emitting diodes (PeLEDs). Here we show that these problems can be solved by introducing both a phosphorescent sensitizer (FIrpic) and an electron transporting material (TmPyPB) into all-inorganic cesium halide perovskite (CsPbBr3). And highly efficient green PeLEDs with full coverage CsPbBr3:TmPyPB:FIrpic film as the emissive layer have been achieved, exhibiting the maximum luminance of 37784 cd/m2, the maximum current efficiency of 22.6 cd/A and the corresponding maximum external quantum efficiency (EQE) of 5.85%, where the EQE is 48-fold to that of bare CsPbBr3 PeLEDs. The enhanced EL performance is attributed to less non-radiative current leakage, better film surface passivation effect, balanced charge carrier injection and transportation, as well as better exciton harvesting. It is believed that our work will provide an effective strategy to further improve EL performance of PeLEDs via better exciton harvesting.

Poly(3,4-ethenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) and graphene oxide (GO) as well as their hybrids have been widely used to prepare hole-transport layer (HTL) for inverted planar perovskite solar cells (PeSCs). However, their acidic nature is detrimental to the stability of PeSC. In this study, we report a simple and general strategy to prepare non-corrosive HTL by treating GO and PEDOT:PSS with ammonia or ammonium (i.e., (NH4)2HPO4), respectively. The PeSC based on ammonia-treated GO (a-GO) yields a power conversion efficiency (PCE) over 14%, remarkably outperforming those with pristine GO (∼12%) or PEDOT:PSS (∼13%). Similar improvement is also observed for the devices with ammonia or ammonium-treated PEDOT:PSS. The mechanism behind such improvement is thoroughly studied, demonstrating the significance of ammonia treatment on the HTL performance. More importantly, the devices based on ammonia-treated HTL exhibit significantly improved stability, as compared to those based on pristine PEDOT:PSS and GO.

Effective hole transport layers (HTLs) are still critical and desirable for the fabrication of high-performance, high-stability and cost-effective polymer solar cells (PSCs). In this work, we report that the graphene oxide (GO) simply modified with CuCl2-doping (GO:CuCl2) can be used as an effective HTL to produce high-performance PSC based on poly[(ethylhexyl-thiophenyl)-benzodithiophene-(ethylhexyl)-thienothiophene]:[6,6]-phenyl C71 butyric acid methyl ester (PTB7-Th: PC71BM). As a result, the average power conversion efficiency (PCE) reaches 7.68%, remarkably higher than that of the device using pristine GO as HTL (7.10%) and comparable to that of the device with conventional HTL of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) (7.69%). UPS measurements suggest that the work function of GO:CuCl2 is slightly increased relative to that of undoped GO. AFM characterizations also reveal a more continuous film morphology for the deposited GO:CuCl2 layer on indium tin oxide (ITO). Such improvements render an ohmic contact as well as a better interfacial contact between the electrode and active layer, yielding improved open-current voltage (Voc), fill factor (FF) and thus enhanced PCE.

In this work, a facile preparation of Cu-Au bimetallic nanoparticles (NPs) with core-shell nanostructures is reported. Importantly, as-prepared Cu-Au NPs are highly stable, solution-processable and exhibit a broad localized surface plasmon resonance (LSPR) band at long wavelengths of 550–850 nm. Highly efficient plasmonic organic solar cells (OSCs) were fabricated by embedding Cu-Au NPs in an anodic poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layer. The average power conversion efficiency (PCE) was enhanced from 3.21% to 3.63% for poly(3-hexylthiophene) (P3HT):phenyl-C 61 -butyric acid methyl ester (PC 61 BM) based devices, from 6.51% to 7.13% for poly[(ethylhexyl-thiophenyl)-benzodithiophene -(ethylhexyl)-thienothiophene](PTB7-th):PC 61 BM based devices and from 7.53% to 8.48% for PTB7-th:PC 71 BM based devices, corresponding to 9.5–13.4% PCE improvement. Such an improvement is very comparable to that (12.5%) obtained in those with plasmonic Au NPs but achieved at lower cost. This study thus demonstrates a novel and cost-effective approach to enhance the photovoltaic performance of OSCs, in combination with the broad-band plasmonic Cu-Au bimetallic nanostructures.

The polymer solar cell (PSC) with Ca/Al electrode always suffers from low stability mainly due to the incorporation of oxygen and moisture-sensitive Ca electron-transport interlayer (ETL). To alleviate this problem, air-stable alternatives to Ca ETL are highly desired. Herein, we report two solution-processable, air-stable, effective and inexpensive ETLs based on potassium-neutralized perylene tetracarboxylic derivative (K 4 PTC) and its rGO composite (rGO-K 4 PTC), respectively. These ETL materials were facilely prepared and characterized by means of UV-vis, FL, FTIR, XPS and UPS. Importantly, both ETLs exhibited a low work function (WF) of 4.0 eV, which well matches the LUMO level of fullerene acceptors and allows their use as ETL in PSCs. As a result, the P3HT and PTB7-th-based devices with respective ETL remarkably outperformed those without ETL yielding increases of ∼35% in power conversion efficiencies (PCEs), which indicates good electron-transporting capabilities of K 4 PTC and rGO-K 4 PTC interlayers. The high-performance PSCs with the ETL gave average PCEs of 6.17–6.18% (for PTB7-th:PC 61 BM-based devices) and 7.26% (for PTB7-th:PC 71 BM-based devices), respectively, fairly comparable to those of Ca/Al devices (6.50% and 7.50%). Furthermore, the rGO-K 4 PTC device exhibited stability higher than that of the K 4 PTC device probably due to the fact that the rGO-K 4 PTC layer can provide more efficient protection for the active layer against degradation. Thus, rGO-K 4 PTC layer might be more suitable for real applications as compared to the K 4 PTC layer.

Understanding the chemical evolution at the interface of organic light-emitting diodes (OLEDs) under working conditions is critical for addressing device failure and further improving performance. In this work, an in-operando approach was developed employing synchrotron-based X-ray absorption spectroscopy (XAS) to investigate the electronic structures and chemical degradation mechanisms of a model tris(8-hydroxyquinoline) aluminum (Alq3)-based OLED device under working condition. The results identify that Mg atoms from the electrode migrate into the Alq3 organic layer under a potential bias and replace Al atom sites, forming the unstable Mgq3 species which lead to device degradation. The findings from the classic and simple model device elucidate the degradation mechanisms occurred at the interface of OLED devices, which may facilitate the development of more efficient and stable OLED devices with complex structures.

To date, doped 2,2,7,7-Tetrakis(N,N-dip-methoxyphenylamine)-9,9-spirobifluorene (Spiro-OMeTAD) is still state-of-the-art hole transport material (HTM) for inverted perovskite solar cells (PeSCs). Nevertheless, hydroscopic dopants usually lead to accelerated degradation of perovskite and hence reduce the device durability especially those based on all-inorganic perovskite. In this work, we report a series of dopant-free mixtures (SpiPA) of hydrophilic Spiro-OMeTAD and hydrophobic poly(triarylamine) (PTAA), which exhibit tunable surface wettability due to the dominant lateral phase separation. When applying them as HTM for inverted CsPbI2Br PeSCs, SpiPA-II based devices yield enhanced efficiency up to 12.52% with significantly reduced hysteresis, as compared to the devices with other mixed HTLs (SpiPA-I, SpiPA-III, SpiPA-IV) and conventional HTLs including pristine Spiro-OMeTAD (10.26%), PTAA (9.05%) and NiOx (10.75%). Additionally, the corresponding mechanism has been studied in detail.

An organic molecule, hexaazatriphenylene hexacarbonitrile (HAT-CN), is found that it can be used not only as a hole-injecting material but also a surface modification material to clean contaminated substrate electrodes for the fabrication of organic electronic devices. As an example, HAT-CN can modify or “clean” indium-tin-oxide (ITO) anode surface in organic light-emitting diodes (OLEDs). Negative effect from ITO surface contamination on the electroluminescence performance of OLEDs can be dramatically reduced with this modification layer. As a result, the OLEDs with the same device architecture but with different ITO surface conditions, even with intentional contamination, can all exhibit substantially identical and superior electroluminescence performance. The surface modification function of this material is feasibly useful for the real fabrications of OLEDs as well as for advanced research on other organic electronic devices.

Although [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) has been widely used as electron transport layer (ETL) for inverted perovskite solar cells (PeSCs), it still remains to be improved. Herein, we report that amphoteric imidazole (IZ) and benzimidazole (BIZ) can act as effective and multifunctional dopants for PC61BM-based ETL. The resultant MAPbI3-xCl3-based PeSCs outperform the devices with pristine PC61BM ETL with power conversion efficiency (PCE) significantly improved from 14.38% to 15.62/16.47%. Detailed mechanism studies demonstrate that IZ and BIZ-doping cause remarkable reduction of ETL surface roughness and significant increase in electrical conductivity of ETL, both of which facilitate the electron transport from perovskite (PVK) and Ag cathode. More importantly, IZ and BIZ as dopants may passivate both Lewis-acid and Lewis-base type defects on the PVK surface due to their amphoteric nature. DFT computations further reveal that BIZ is a better Lewis-base and Lewis-acid than IZ due to its larger π-conjugation, which thus makes it a superior dopant over IZ. In addition, the PeSCs with PC61BM:BIZ based ETL display enhanced device stability by retarding the I− anion migration from PVK to Ag cathode.

[6,6]-Phenyl-C61-butyric acid methylester (PC61BM) has been widely used as electron transport material (ETM) for both organic-inorganic hybrid and all inorganic perovskite solar cells (PeSCs) with inverted structure. However, PC61BM still remains to be improved due to its low electrical conductivity and inferior passivation effect towards perovskite. In this work, we synthesize two perfluorophenyl-substituted fulleropyrrolidines, 2-(perfluorophenyl)-5-phenyl-C60-fulleropyrrolidine (FP-i) and 2,5-bis-(perfluorophenyl)-C60-fulleropyrrolidine (FP-ii) via a modified 1,3-dipolar cycloaddition reaction. FP-i and FP-ii are introduced into inverted PeSCs based on organic-inorganic hybrid and all inorganic perovskites (CH3NH3PbCl3-xIx and CsPbI2Br) as ETMs. The PeSCs based on FP-i and FP-ii display good photovoltaic performance and device stability, which are superior or comparable to those with PC61BM. The mechanism studies reveal that FP-i and FP-ii possess higher electrical conductivity, more significant passivation capacity and enhanced hydrophobicity but slightly lower low unoccupied molecular orbital (LUMO) levels. These results suggest that FP-i and FP-ii are universal ETMs for both organic-inorganic hybrid and all inorganic PeSCs, which are better or comparable to conventional ETM of PC61BM.

In this work, we demonstrate three kinds of intermediate connectors (ICs) having a general configuration of “LiNH2-doped 4,7-diphenyl-1,10-phenanthroline (BPhen)/hole injection layer (HIL)/N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine (NPB)”, in which the HIL is 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN), MoO3 or MoO3-doped NPB, respectively. Tandem organic light-emitting devices (OLEDs), vertically stacking two electroluminescence units, are fabricated using these intermediate connectors in between. The results show that, higher power efficiency is achievable in the cases of utilizing HAT-CN and MoO3-doped NPB as HILs in the intermediate connectors versus MoO3, whereas higher current efficiency can be obtained in the cases of using MoO3 and MoO3-doped NPB versus HAT-CN. We use the current density–voltage and low frequency differential capacitance–voltage measurements and find that the HILs primarily influence the voltage drop and the charge generation capability of intermediate connectors. The correlation between the effectiveness of intermediate connectors and the performances of tandem OLEDs is established, which can shed light on choosing suitable component materials to optimize the intermediate connectors.

A high efficiency phosphorescent organic light-emitting diode (OLED) has been fabricated by introducing a double exciton-blocking layer (d-EBL) between the hole-transporting layer and the light-emitting layer in the device. The device exhibits a yellow emission with a maximum current efficiency of 58.5 cd/A at 117 cd/m 2 , corresponding to the power efficiency of 50.9 lm/W, which is two times improved compared with that of devices having only one traditional single exciton-blocking layer (s-EBL). The efficiency improvement has been investigated through the electroluminescence (EL) spectral analyses in the phosphorescent guest-doped and the non-doped OLEDs. The results demonstrate that the electrons are blocked and the excitons are confined more effectively in the d-EBL-based devices than that in the s-EBL-based devices. In addition, over two times improvement in the lifetime is also achieved in the devices with the d-EBL compared with the devices having a traditional s-EBL.