Search

To attain commercial viability, perovskite solar cells (PSCs) have to be reasonably priced, highly efficient, and stable for a long period of time. Although a new record of a certified power conversion efficiency (PCE) value over 25% was achieved, PSC performance is limited by the lack of hole-transporting materials (HTMs), which extract positive charges from the light-absorbing perovskite layer and carry them to the electrode. Here, we report spirobifluorene-based HTMs with finely tuned energy levels, high glass-transition temperature, and excellent charge mobility and conductivity enabled by molecularly engineered enamine arms. HTMs are synthesized using simple condensation chemistry, which does not require costly catalysts, inert reaction conditions, and time-consuming product purification procedures. Enamine-derived HTMs allow the fabrication of PSCs reaching a maximum PCE of 19.2% and stability comparable to spiro-OMeTAD. This work demonstrates that simple enamine condensation reactions could be used as a universal path to obtain HTMs for highly efficient and stable PSCs.

Bismuth films with thicknesses between 6 and ∼30 nm were grown on Si (111) substrate by molecular beam epitaxy (MBE). Two main phases of bismuth — α-Bi and β-Bi — were identified from high-resolution X-ray diffraction (XRD) measurements. The crystal structure dependencies on the layer thicknesses of these films were analyzed. β-Bi layers were epitaxial and homogenous in lateral regions that are greater than 200 nm despite the layer thickness. Further, an increase in in-plane 2θ values showed the biaxial compressive strain. For comparison, α-Bi layers are misoriented in six in-plane directions and have β-Bi inserts in thicker layers. That leads to smaller (about 60 nm) lateral crystallites which are compressively strained in all three directions. Raman measurement confirmed the XRD results. The blue-sift of Raman signals compared with bulk Bi crystals occurs due to the phonon confinement effect, which is larger in the thinnest α-Bi layers due to higher compression.

Recent progress of vapor-deposited perovskite solar cells (PSCs) has proved the feasibility of this deposition method in achieving promising photovoltaic devices. For the first time, it is probed the versatility of the co-evaporation process in creating perovskite layers customizable for different device architectures. A gradient of composition is created within the perovskite films by tuning the background chamber pressure during the growth process. This method leads to co-evaporated MAPbI3 film with graded Fermi levels across the thickness. Here it is proved that this growth process is beneficial for p-i-n PSCs as it can guarantee a favorable energy alignment at the charge selective interfaces. Co-evaporated p-i-n PSCs, with different hole transporting layers, consistently achieve power conversion efficiency (PCE) over 20% with a champion value of 20.6%, one of the highest reported to date. The scaled-up p-i-n PSCs, with active areas of 1 and 1.96 cm2, achieved the record PCEs of 19.1% and 17.2%, respectively, while the flexible PSCs reached a PCE of 19.3%. Unencapsulated PSCs demonstrate remarkable long-term stability, retaining ≈90% of their initial PCE when stored in ambient for 1000 h. These PSCs also preserve over 80% of their initial PCE after 500 h of thermal aging at 85 °C. © 2021 Wiley-VCH GmbH

Perovskite solar cells deliver high efficiencies, but are often made from high-cost bespoke chemicals, such as the archetypical hole-conductor, 2,2′,7,7′-tetrakis(N,N-di-p-methoxy-phenylamine)-9-9′-spirobifluorene (spiro-OMeTAD). Herein, new charge-transporting carbazole-based enamine molecules are reported. The new hole conductors do not require chemical oxidation to reach high power conversion efficiencies (PCEs) when employed in n-type-intrinsic-p-type perovskite solar cells; thus, reducing the risk of moisture degrading the perovskite layer through the hydrophilicity of oxidizing additives that are typically used with conventional hole conductors. Devices made with these new undoped carbazole-based enamines achieve comparable PCEs to those employing doped spiro-OMeTAD, and greatly enhanced stability under 85 °C thermal aging; maintaining 83% of their peak efficiency after 1000 h, compared with spiro-OMeTAD-based devices that degrade to 26% of the peak PCE within 24 h. Furthermore, the carbazole-based enamines can be synthesized without the use of organometallic catalysts and complicated purification techniques, lowering the material cost by one order of magnitude compared with spiro-OMeTAD. As a result, we calculate that the overall manufacturing costs of future photovoltaic (PV) modules are reduced, making the levelized cost of electricity competitive with silicon PV modules.

ZnO materials have been at the centre of many studies for decades. Doping of ZnO by lithium atoms is a prospective approach for compensation of n-type conductivity in the unintentionally doped ZnO aimed at obtaining p-type semiconductor. In this study, we have synthesized ZnO rod-like powders doped with lithium ions (0–0.65 atom%) by the new microwave-assisted solvothermal method in order to obtain greater photoluminescence intensity of ZnO emissions in the UV region. The obtained powders contain nanoparticles from 20 nm up to 250 nm depending on Li content. X-ray diffractometry and Raman spectroscopy were employed to characterise the structure of ZnO powders, scanning electron microscopy was used to determine the morphology, and most importantly the photoluminescence technique was used to investigate the optical properties of the obtained materials. As a result, the photoluminescence intensity has been increased up to an order of magnitude with the Li content in the ZnO crystals. The increase of the excitation laser power has led to an increased carrier lifetime and photoluminescence response intensity that is observed for all the samples.

In a short period of time, the rapid development of perovskite solar cells attracted a lot of attention in the science community with the record for power conversion efficiency being broken every year. Despite the fast progress in power conversion efficiency there are still many issues that need to be solved before starting large scale commercial applications, such as, among others, the difficult and costly synthesis and usage of toxic solvents for the deposition of hole transport materials (HTMs). We herein report new enamine-based charge transport materials obtained via a simple one step synthesis procedure, from commercially available precursors and without the use of expensive organometallic catalysts. The developed materials demonstrated rapid loss of mass during thermogravimetry analysis suggesting that they could be processed not only using solution processing but also via vacuum deposition. Furthermore, all HTMs demonstrated high charge carrier mobility with H2 possessing the highest mobility of 2.5 × 10−2 cm2 V−1 s−1 under strong electric fields. The investigated materials were employed in vacuum-deposited p–i–n perovskite solar cells and champion devices with enamine H2 demonstrate a PCE of 18.4%.

One of the obstacles to the commercialization of perovskite solar cells (PSCs) is the high price and morphological instability of the most common hole-transporting material (HTM) Spiro-OMeTAD. Herein, a novel HTM, termed V1160, based on four N,N '-bis(3-methylphenyl)-N,N '-diphenylbenzidine (TPD)-type fragments, fused by a Troger's base core, is synthesized and successfully applied in PSCs. Investigation of the optical, thermal, and photoelectrical properties shows that V1160 is a suitable candidate for application as an HTM in PSCs. A promising power conversion efficiency (PCE) of over 18% is demonstrated, which is only slightly lower than that of Spiro-OMeTAD. Moreover, V1160-based devices exhibit improved performances in dopant-free configurations and superior stability. Favorable morphological properties in combination with a simple synthesis make V1160 and related materials promising for HTM applications.

The search for new classes of hole transporting materials (HTMs) is a very important task on the way towards commercialization of perovskite solar cells (PSCs). In this work, the synthesis and performance in PSCs of new enamine-based HTMs are presented. The synthesis scheme is very short, consisting of only one step, starting from commercially available aromatic amines. Moreover, the reaction does not require metal catalysts and is based on condensation chemistry with water as a by-product. It was shown that PSCs with such materials reach high power conversion efficiencies (PCE), with the highest PCE of 19% achieved for the V1021-based device. This work establishes enamines as a very promising class of materials for application in PSCs.

A new cross-linkable monomer containing 1,3-diphenylethenylcarbazolyl-based hole-transporting moieties and four reactive epoxy groups, was prepared by a multistep synthesis route from 1,3-bis(2,2-diphenylethenyl)-9H-carbazol-2-ol and its application for the in situ formation of cross-linked hole transporting layers was investigated. A high concentration of flexible aliphatic epoxy chains ensures good solubility and makes this compound an attractive cross-linking agent. The synthesized compounds were characterized by various techniques, including differential scanning calorimetry, xerographic time of flight, and electron photoemission in air methods.

Metal‐halide perovskites offer great potential to realize low‐cost and flexible next‐generation solar cells. Low‐temperature‐processed organic hole‐transporting layers play an important role in advancing device efficiencies and stabilities. Inexpensive and stable hole‐transporting materials (HTMs) are highly desirable toward the scaling up of perovskite solar cells (PSCs). Here, a new group of aniline‐based enamine HTMs obtained via a one‐step synthesis procedure is reported, without using a transition metal catalyst, from very common and inexpensive aniline precursors. This results in a material cost reduction to less than 1/5 of that for the archetypal spiro‐OMeTAD. PSCs using an enamine V1091 HTM exhibit a champion power conversion efficiency of over 20%. Importantly, the unsealed devices with V1091 retain 96% of their original efficiency after storage in ambient air, with a relative humidity of 45% for over 800 h, while the devices fabricated using spiro‐OMeTAD dropped down to 42% of their original efficiency after aging. Additionally, these materials can be processed via both solution and vacuum processes, which is believed to open up new possibilities for interlayers used in large‐area all perovskite tandem cells, as well as many other optoelectronic device applications.

In this paper, a superior-quality InN/p-GaN interface grown using pulsed metalorganic vapor-phase epitaxy (MOVPE) is demonstrated. The InN/p-GaN heterojunction interface based on high-quality InN (electron concentration 5.19 &times, 1018 cm&minus, 3 and mobility 980 cm2/(V s)) showed good rectifying behavior. The heterojunction depletion region width was estimated to be 22.8 nm and showed the ability for charge carrier extraction without external electrical field (unbiased). Under reverse bias, the external quantum efficiency (EQE) in the blue spectral region (300&ndash, 550 nm) can be enhanced significantly and exceeds unity. Avalanche and carrier multiplication phenomena were used to interpret the exclusive photoelectric features of the InN/p-GaN heterojunction behavior.

In present study five synthesized organic semiconductor compounds have been used for fabrication of the planar metal / organic semiconductor / metal structures. Both top electrode and bottom electrode configurations were used. Current-voltage (I-V) characteristics of the samples were investigated. Effect of the hysteresis of the I-V characteristics was observed for all the investigated samples. However, strength of the hysteresis was dependent on the organic semiconductor used. Study of I-V characteristics of the top contact Al/AT-RB-1/Al structures revealed, that in (0 – 500) V voltages range average current of the samples measured in air is only slightly higher than current measured in nitrogen ambient. Deposition of the ultra-thin diamond like carbon interlayer resulted in both decrease of the hysteresis of I-V characteristics of top contact Al/AT-RB-1/Al samples. However, decreased current and decreased slope of the I-V characteristics of the samples with diamond like carbon interlayer was observed as well. I-V characteristic hysteresis effect was less pronounced in the case of the bottom contact metal/organic semiconductor/metal samples. I-V characteristics of the bottom contact samples were dependent on electrode metal used.DOI: http://dx.doi.org/10.5755/j01.ms.19.1.3816

In this research 300 fs pulses of Yb:KGW laser has been applied to form electron transport layer TiO2 of Grӓtzel type organic solar cells (OSC) with different surface roughness. Profiler, AFM, SEM has been used to define surfaces. Scattering of 532 nm wavelength light from ablated regions has been measured. OSC have been formed onto TiO2 and I-V characteristics have been measured. Investigation results demonstrated that laser treatment of TiO2 has impact to the I-V dependencies of OSC. 1. Motivation

Light induced transient grating technique is applied to study the recombination and transport properties of the excess carriers in the iron-doped highly resistive GaN/sapphire epilayers, grown by MOCVD and doped using the modulation doping technique. Carrier lifetime, ambipolar diffusion coefficient, and threshold of the stimulated recombination are compared between Fe-doped (NFe

We present nonlinear optical four-wave mixing (FWM) and microwave absorption (MWA) techniques for the monitoring of nonequilibrium carrier dynamics in CdTe epitaxial layers grown on GaAs by either hydrogen transport (H 2 T) or metalorganic vapour phase epitaxy, as well as in a sub-surface region of GaAs and CdTe single crystals. For the excitation, picosecond YAG or parametric laser pulses were used to record free carrier surface gratings with a variable thickness of the excited region, while ns-YAG pulses were utilized for the edge excitation of the heterostructures via a 3 μm diameter fiber. Fast transients of light diffraction allowed to determine the values of the diffusion coefficient, surface and bulk recombination velocities of the highly excited sample, and to study the ageing effect of MOVPE-grown epilayers. Asymptotic values of the carrier decay of about 2-4 μs were found in thick epilayers by MWA and attributed to a linear-recombination in thick CdTe epilayers grown by H 2 T-VPE.