Electron and hole transport layers have critical impacts on the overall performance of perovskite solar cells (PSCs). Herein, for the first time, a solution-processed cobalt (Co)-doped NiO film was fabricated as the hole transport layer in inverted planar PSCs, and the solar cells exhibit 18.6% power conversion efficiency. It has been found that an appropriate Co-doping can significantly adjust the work function and enhance electrical conductivity of the NiO film. Capacitance-voltage ( C- V) spectra and time-resolved photoluminescence spectra indicate clearly that the charge accumulation becomes more pronounced in the Co-doped NiO -based photovoltaic devices; it, as a consequence, prevents the nonradiative recombination at the interface between the Co-doped NiO and the photoactive perovskite layers. Moreover, field-dependent photoluminescence measurements indicate that Co-doped NiO -based devices can also effectively inhibit the radiative recombination process in the perovskite layer and finally facilitate the generation of photocurrent. Our work indicates that Co-doped NiO film is an excellent candidate for high-performance inverted planar PSCs.

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In this article, two different types of spacer cations, 1,4‐butanediamonium (BDA2+) and 2‐phenylethylammonium (PEA+) are co‐used to prepare the perovskite precursor solutions with the formula of (BDA)1‐a(PEA2)aMA4Pb5X16. By simply mixing the two spacer cations, the self‐assembled polycrystalline films of (BDA)0.8(PEA2)0.2MA4Pb5X16 are obtained, and BDA2+ is located in the crystal grains and PEA+ is distributed on the surface. The films display a small exciton binding energy, uniformly distributed quantum wells and improved carrier transport. Besides, utilizing mixed spacer cations also induces better crystallinity and vertical orientation of 2D perovskite (BDA)0.8(PEA2)0.2MA4Pb5X16 films. Thus, a power conversion efficiency (PCE) of 17.21% is achieved in the optimized perovskite solar cells with the device structure of ITO/PEDOT:PSS/Perovskite/PCBM/BCP/Ag. In addition, the complementary humidity and thermal stability are obtained, which are ascribed to the enhanced interlayer interaction by BDA2+ and improved moisture resistance by the hydrophobic group of PEA+. The encapsulated devices are retained over 95% or 75% of the initial efficiency after storing 500 h in ambient air under 40 ± 5% relative humidity or 100 h in nitrogen at 60 °C.

The geometries of acceptors based on perylene diimides (PDIs) are important for improving the phase separation and charge transport in organic solar cells. To fine-tune the geometry, biphenyl, spiro-bifluorene, and benzene were used as the core moiety to construct quasi-three-dimensional nonfullerene acceptors based on PDI building blocks. The molecular geometries, energy levels, optical properties, photovoltaic properties, and exciton kinetics were systematically studied. The structure-performance relationship was discussed as well. Owing to the finest phase separation, the highest charge mobility and smallest nongeminate recombination, the power conversion efficiency of nonfullerene solar cells using PDI derivatives with biphenyl core (BP-PDI) as acceptor reached 7.3% when high-performance wide band gap donor material poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b']dithiophene))-alt-(5,5-(1',3'-di-2-thienyl-5',7'-bis(2-ethylhexyl)benzo[1',2'-c:4',5'-c']dithiophene-4,8-dione))] was blended.

Violet light-emitting diodes (LEDs) are widely utilized for solid-state lighting, bacteria sterilization, and so on. Herein, the nontoxic and earth-abundant Ce 3+ ion with intrinsic strong violet emission is introduced to substitute Pb 2+ in CsPbBr 3 perovskite for electrically driven PeLEDs. Cs 3 CeBr 6 possesses a zero-dimensional photoactive site with a high photoluminescence quantum yield of ≈90% for both crystals and films. The excited-state lifetime of ≈28 ns enabled by the spin-and parity-allowed Ce-5d → Ce-4f transition is considerably faster than other lanthanide-based luminescent centers. The violet LEDs based on thermally evaporated Cs 3 CeBr 6 films display color-stable spectra with a maximum EQE of 0.46%, representing the first Cs 3 CeBr 6 LED and one of the most efficient violet PeLEDs. Moreover, a white LED with standard color coordinates of (0.339, 0.343) is constructed by combining Cs 3 CeBr 6 -based violet PeLEDs with yellow phosphor downconverters. Our work will motivate further exploration of diverse lanthanide-based perovskites for LEDs and other optoelectronics.

This study reports an effective amidine-type n-dopant of 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) that can universally dope electron acceptors, including PC 61 BM, N2200, and ITIC, by mixing the dopant with the acceptors in organic solvents or exposing the acceptor films in the dopant vapor. The doping mechanism is due to its strong electron-donating property that is also confirmed via the chemical reduction of PEDOT:PSS (yielding color change). The DBU doping considerably increases the electrical conductivity and shifts the Fermi levels up of the PC 61 BM films. When the DBU-doped PC 61 BM is used as an electron-transporting layer in perovskite solar cells, the n-doping removes the "S-shape" of J-V characteristics, which leads to the fill factor enhancement from 0.54 to 0.76. Furthermore, the DBU doping can effectively lower the threshold voltage and enhance the electron mobility of PC 61 BMbased n-channel field-effect transistors. These results show that the DBU can be a promising n-dopant for solution-processed electronics.

Excited states in organic light-emitting diodes (OLEDs) are inevitably formed with both singlets and triplets under electrical excitation. Singlets and triplets are allowed and forbidden to recombine, respectively, due to spin selection rule. It has been shown that the triplets can be almost 100% converted into singlets in thermally activated delayed fluorescence (TADF) molecules based on the design of chemically combining donor and acceptor moieties to enable intramolecular chargetransfer states. [1][2][3][4] Recently, various TADFmolecule-based OLEDs with extremely high external quantum efficiency (EQE) exceeding 35% have been successfully demonstrated. [5,6] Similarly, high EQEs can also be conveniently realized by physically mixing donor and acceptor components to form intermolecular charge-transfer states in exciplex systems, where the nonradiative triplets are also largely converted into radiative singlets. The advantages and versatile applications of exciplex systems for giving high-efficiency OLEDs have been highlighted recently. [7] More significantly, OLEDs with exciplex-forming systems as emitting layer have been reported to achieve EQE higher than 19%, [8][9][10] manifesting their bright and promising prospects in OLED technology based on physically Experimental studies to reveal the cooperative relationship between spin, energy, and polarization through intermolecular charge-transfer dipoles to harvest nonradiative triplets into radiative singlets in exciplex lightemitting diodes are reported. Magneto-photoluminescence studies reveal that the triplet-to-singlet conversion in exciplexes involves an artificially generated spin-orbital coupling (SOC). The photoinduced electron parametric resonance measurements indicate that the intermolecular charge-transfer occurs with forming electric dipoles (D +• →A −• ), providing the ionic polarization to generate SOC in exciplexes. By having different singlet-triplet energy differences (ΔE ST ) in 9,9′-diphenyl-9H,9′H-3,3′-bicarbazole (BCzPh):3′,3′″,3′″″-(1,3,5-triazine-2,4,6-triyl) tris(([1,1′-biphenyl]-3-carbonitrile)) (CN-T2T) (ΔE ST = 30 meV) andBCzPh:bis-4,6-(3,5-di-3-pyridylphenyl)-2-methyl-pyrimidine (B3PYMPM) (ΔE ST = 130 meV) exciplexes, the SOC generated by the intermolecular charge-transfer states shows large and small values (reflected by different internal magnetic parameters: 274 vs 17 mT) with high and low external quantum efficiency maximum, EQE max (21.05% vs 4.89%), respectively. To further explore the cooperative relationship of spin, energy, and polarization parameters, different photoluminescence wavelengths are selected to concurrently change SOC, ΔE ST , and polarization while monitoring delayed fluorescence. When the electron clouds become more deformed at a longer emitting wavelength due to reduced dipole (D +• →A −• ) size, enhanced SOC, increased orbital polarization, and decreased ΔE ST can simultaneously occur to cooperatively operate the triplet-to-singlet conversion.

Quasi-2D Ruddlesden−Popper perovskites exhibit excellent photostability/environmental stability. However, the main drawback is their relatively low photovoltaic properties compared with three-dimensional perovskites. Herein, we demonstrated that chlorine-based additives via adjusting the proportion of PbI 2 and PbCl 2 in the precursor (BA) 2 (MA) 3 Pb 4 I 13 (n = 4) solutions show an optimized device performance of over 15%, and the devices exhibit much improved humidity stability. Upon PbCl 2 addition, the quasi-2D perovskites have larger and more compact grains, which result in high quality of films. The photoluminescence gives rise to a much prolonged lifetime under the PbCl 2 additive, indicating fewer trap states to reduce the nonradiative recombination. The capacitance characteristics confirm that the PbCl 2 additive can largely decrease the trap states in quasi-2D perovskite films. The capacitance−voltage characteristics indicate that using the PbCl 2 additive decreases the charge accumulation toward increasing the charge collection in quasi-2D perovskite solar cells. Our work indicates that the addition of PbCl 2 is an effective method to improve the device performance by reducing trap states and increasing charge collection toward developing high-performance quasi-2D perovskite devices.