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Perovskite solar cells (PSCs) have received a remarkable attention compared to the other types of solar cells due to their high carrier mobility, low recombination rate, and rapid increase in terms of efficiency in short time. However, two essential parameters being stability and cost are still challenging with these kinds of solar cells. Hole transport materials (HTMs) play an important role in PSCs as they can be effective in the charge transportation, determining the device stability and having a large share of cell costs, and overall resulting in the enhancement of open-circuit voltage (V-oc), short-circuit current (J(sc)), and fill factor (FF). In addition to the organic HTMs which are widely used in PSCs, various inorganic HTMs mainly divided into the oxide and sulfide subgroups, have been developed in order to improve both stability and cost of PSCs. Herein, we provide an overview of the diverse types of HTMs, from organic to inorganic, especially oxide and sulfide inorganic HTMs and investigate the physical properties, synthesis, and their applications in various PSCs for both mesoporous and planar structure in the hope of encouraging further research and the optimization of these materials.

The backreaction in dye-sensitized solar cells (DSSCs) was long ago recognized as one of the main causes of decreasing energy conversion efficiency. Hence, many different approaches have been attempted to reduce the backreaction. In the present work, we use nitrogen additives in the electrolyte to reduce the backreaction with TiO2 and I3−. Intensity-modulated photocurrent/photovoltage (IMPS/IMVS) and charge extraction (CE) techniques are used to obtain information on the dynamics of charge carriers in DSSCs assembled with and without nitrogen additives. The passivation process occurring on the nanoparticles, which is promoted by the additives, prevents recombination but does not change the electron transport time. Therefore, the description of transport and electron recombination kinetics in DSSCs is well established in this work with the emerging IMPS, IMVS, and CE techniques.

Perovskite nanocrystals (PeNCs) are known for their use in numerous optoelectronic applications. Surface ligands are critical for passivating surface defects to enhance the charge transport and photoluminescence quantum yields of the PeNCs. Herein, we investigated the dual functional abilities of bulky cyclic organic ammonium cations as surface-passivating agents and charge scavengers to overcome the lability and insulating nature of conventional long-chain type oleyl amine and oleic acid ligands. Here, red-emitting hybrid PeNCs of the composition CsxFA(1−x)PbBryI(3−y) are chosen as the standard (Std) sample, where cyclohexylammonium (CHA), phenylethylammonium (PEA) and (trifuluoromethyl)benzylamonium (TFB) cations were chosen as the bifunctional surface-passivating ligands. Photoluminescence decay dynamics showed that the chosen cyclic ligands could successfully eliminate the shallow defect-mediated decay process. Further, femtosecond transient absorption spectral (TAS) studies uncovered the rapidly decaying non-radiative pathways; i.e., charge extraction (trapping) by the surface ligands. The charge extraction rates of the bulky cyclic organic ammonium cations were shown to depend on their acid dissociation constant (pKa) values and actinic excitation energies. Excitation wavelength-dependent TAS studies indicate that the exciton trapping rate is slower than the carrier trapping rate of these surface ligands.

Sb2(S, Se)3 solar cells have shown great promise due to the advantages of low cost, non-toxic and high stability. However, traditional devices commonly use noble metal as the back electrode, which not only increases device cost but also limits device stability. Herein, carbon materials are used to replace the noble metals in Sb2(S, Se)3 solar cells. In addition, to grow high-quality Sb2(S, Se)3 films, a two-step hydrothermal method was developed. The carbon-based Sb2(S, Se)3 solar cells based on the above film achieved a power conversion efficiency (PCE) of 2.76%. After inserting a stable P3HT layer at the Sb2(S, Se)3 film/carbon interface, hole extraction was enhanced and the PCE was promoted to 4.15%. This work brings out a promising route to produce emerging solar cells with cost-effective and stable materials.

Non‐fullerene acceptors are currently a hot research area in the development of organic solar cells (OSCs). At present, the‐state‐of‐the‐art power conversion efficiency (PCE) of non‐fullerene organic solar cells (NF‐OSCs) with single and multiple‐junction has surpassed 18% and 19%, respectively. The cathode interlayer (CIL) plays a significant role in the improvement of PCE and the stability of OSCs. Recently, a large number of CIL materials have been employed in OSCs. This review summarizes the recent progress of CIL materials and systematically describes their impact on the device efficiency and stability in single‐junction NF‐OSCs. Firstly, the functions, key requirements, and distinctive features of CILs when used in NF‐OSCs are summarized. Afterward, some big families of materials including metal oxides, metal salts/complexes, small molecules, polymers, composites/hybrids are presented as CIL for NF‐OSCs. Finally, the scale‐up techniques, conclusion, and future challenges regarding CIL in NF‐OSCs are elucidated.

The photocurrent density-voltage (J(V)) curve is the fundamental characteristic to assess opto-electronic devices, in particular solar cells. However, it only yields information on the performance integrated over the entire active device area. Here, a method to determine a spatially resolved photocurrent image by voltage-dependent photoluminescence microscopy is derived from basic principles. The opportunities and limitations of the approach are studied by the investigation of III-V and perovskite solar cells. This approach allows the real-time assessment of the microscopically resolved local J(V) curve, the steady-state Jsc, as well as transient effects. In addition, the measurement contains information on local charge extraction and interfacial recombination. This facilitates the identification of regions of non-ideal charge extraction in the solar cells and enables to link these to the processing conditions. The proposed technique highlights that, combined with potentiostatic measurements, luminescence microscopy turns out to be a powerful tool for the assessment of performance losses and the improvement of solar cells.

Herein, a strong short-circuit current density (JSC) loss is observed when using phenetylammonium iodide (PEAI) as n-side passivation in p-i-n perovskite solar cells. Comparing experiments with drift–diffusion simulations, different hypotheses for the origin of the JSC loss are presented and evaluated. Whereas the optical properties of the investigated cell stack remain unchanged, the internal quantum efficiency of the PEAI-based devices decreases drastically. Strong bulk doping and interface traps are ruled out as the origin of the charge extraction limitation. High-spatial resolution photoluminescence (PL) spectroscopy directly images the inhomogeneity of the PEAI-based quasi-2D perovskite wide-bandgap interlayer, which is found to be crucial for the observed JSC loss. A 2D drift-diffusion model implemented with mobile ions and an inhomogeneous electron transport layer reproduces the experimental behavior accurately. The ionic space charge distribution under short circuit reduces the effective charge-carrier diffusion length, hindering charge transport toward those domains in the perovskite-electron transport layer interface where electrons can be extracted efficiently. A longer charge-carrier lifetime reduces the JSC loss, highlighting the importance of suppressed non-radiative bulk recombination, not only for achieving high open-circuit voltages, but also for efficient charge extraction.

Organic electronic devices invariably involve transfer of charge carriers between the organic layer and at least one metal electrode, and they are sensitive to the local properties of the organic film at those interfaces. Here, we demonstrate a new approach for using an advanced technique called surface-enhanced raman spectroscopy (SERS) to quantitatively probe interfacial properties relevant to charge injection/extraction. Exploiting the evanescent electric field generated by a ∼7 nm thick layer of evaporated silver, Raman scattering from nearby molecules is enhanced by factors of 10-1000× and limited by a distance dependence with a measured decay length of only 7.6 nm. When applied to the study of an all-polymer 1:1 blend of P3HT and F8TBT used in organic solar cells, we find that the as-cast film is morphologically suited to charge extraction in inverted devices, with a top (anode) interface very rich in hole-transporting P3HT (74.5%) and a bottom (cathode) interface slightly rich in electron-transporting F8TBT (55%). While conventional, uninverted P3HT:F8TBT devices are reported to perform poorly compared to inverted devices, their efficiency can be improved by thermal annealing but only after evaporation of a metallic top electrode. This is explained by changes in composition at the top interface: annealing prior to silver evaporation leads to a greater P3HT concentration at the top interface to 83.3%, exaggerating the original distribution that favored inverted devices, while postevaporation annealing increases the concentration of F8TBT at the top interface to 34.8%, aiding the extraction of electrons in a conventional device. By nondestructively probing buried interfaces, SERS is a powerful tool for understanding the performance of organic electronic devices.

Quantum dot (QD) solar cells based on different materials have received a noticeable interest during the past ten years; however, their efficiency and stability are still the main drawback of this technology, which leads to a lack of performance of these devices. There are several electron loss (and efficiency) processes involved after photon absorption, but perhaps the main issue is with the electron recombination after excitation of the surface. In this paper, we have studied the dependence of short-circuit photocurrent of TiO2 nanotubes with varying amounts of CdS QDs deposited by the successive ionic layer adsorption and reaction method. We have found that there is an optimum coverage of CdS in order to achieve the maximum photocurrent value. This behavior is explained and characterized in terms of prevailing recombination processes at higher CdS coverage, where quantum confinement becomes less important. By using the charge extraction method, we could determine the time dependence of electrode charge and indicates that the back reaction of electrons with the redox electrolyte present in solution is of the first order in electron density and that it originates from the electrons present in the TiO2 conduction band. Fil: Vazquez, Cecilia Irene. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Baruzzi, Ana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Iglesias, Rodrigo Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina

Establishing the color of incident light is essential for many applications, such as machine vision, but generally requires either a dispersive component or multiple spectrally selective photodetectors. In contrast, here an incident spectrum is parametrized using a single broadband organic photodiode (OPD). This is achieved by exploiting the incident wavelength dependence of charge extraction caused by optically induced trap states in a metal oxide electron extraction layer, which results in an atypical spectral dependence of the reverse bias photocurrent density vs voltage (J–V) characteristics. Such dependence is augmented by confining the active layer within an optical microcavity to influence the light absorption profile and thus metal oxide trap state density. The average wavelength of an (approximately normally distributed) incident spectrum is then calculated to within ≈5 nm by algorithmically minimizing the difference between a measured J–V curve and one determined from the overlap integral of a trial spectrum with previously acquired voltage bias dependent external quantum efficiency (EQE) spectra.

The enhancement of interfacial charge collection efficiency using buffer layers is a cost‐effective way to improve the performance of organic photovoltaic devices (OPVs) because they are often universally applicable regardless of the active materials. However, the availability of high‐performance buffer materials, which are solution‐processable at low temperature, are limited and they often require burdensome additional surface modifications. Herein, high‐performance ZnO based electron transporting layers (ETLs) for OPVs are developed with a novel g‐ray‐assisted solution process. Through careful formulation of the ZnO precursor and g‐ray irradiation, the pre‐formation of ZnO nanoparticles occurs in the precursor solutions, which enables the preparation of high quality ZnO films. The g‐ray assisted ZnO (ZnO‐G) films possess a remarkably low defect density compared to the conventionally prepared ZnO films. The low‐defect ZnO‐G films can improve charge extraction efficiency of ETL without any additional treatment. The power conversion efficiency (PCE) of the device using the ZnO‐G ETLs is 11.09% with an open‐circuit voltage (V OC), short‐circuit current density ( J SC), and fill factor (FF) of 0.80 V, 19.54 mA cm‐2, and 0.71, respectively, which is one of the best values among widely studied poly[4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b;4,5‐b′]dithiophene‐2,6‐diyl‐alt‐(4‐(2‐ethylhexyl)‐3‐fluorothieno[3,4‐b]thiophene‐)‐2‐carboxylate‐2‐6‐diyl)]: [6,6]‐phenyl‐C71‐butyric acid methyl ester (PTB7‐Th:PC71BM)‐based devices.

The performance of organic photovoltaic devices (OPV) with nanostructured polymer:perylene diimide (PDI) photoactive layers approaches the levels of the corresponding polymer:fullerene systems. Nevertheless, a coherent understanding of the difficulty for PDI-based OPV devices to deliver high power conversion efficiencies remains elusive. Here we perform a comparative study of a set of four different polymer:PDI OPV model systems. The different device performances observed are attributed to differences in the nanostructural motif of these composites, as determined by wide-angle X-ray scattering (WAXS) measurements. Long-range structural order in the PDI domain dictates (i) the stabilization energy and (ii) the concentration of the PDI excimers in the composites. The quenching of the PDI excimer photoluminescence (PL) is found to be insensitive to the former, but it depends on the latter. High PL quenching occurs for the low concentration of PDI excimers that are formed in PDI columns with a length comparable to the PDI excimer diffusion length. The stabilization of the PDI excimer state increases as the long-range order in the PDI domains improves. The structural order of the PDI domains primarily affects charge transport. Electron mobility reduces as the size of the PDI domain increases, suggesting that well-ordered PDI domains suffer from poor electronic connectivity. WAXS further reveals the presence of additional intermolecular PDI interactions, other than the direct face-to-face intermolecular coupling, that introduce a substantial energetic disorder in the polymer:PDI composites. Conventional device architectures with hole-collecting ITO/PEDOT:PSS bottom electrodes are compared with inverted device architectures bearing bottom electron-collecting electrodes of ITO/ZnO. In all cases the ZnO-functionalized devices surpass the performance of the conventional device analogues. X-ray photoelectron spectroscopy explains that in PEDOT:PSS-functionalized devices, the PDI component preferentially segregates closer to the hydrophilic PEDOT:PSS electrode, thus impeding the efficient charge extraction and limiting device photocurrent.

Two new porphyrins that incorporate thiophene substituents as spacers between the conjugated porphyrin core and the anchoring cyanoacrylate group have been synthesised. The two dyes differ in the number of thiophene bridges; porphyrin 1a has only one thiophene group and porphyrin 1b has two thiophene rings connected by a double bond. The measured light-to-energy conversion efficiencies in 1a and 1b were assessed using two different electrolytes, LP1 and LP2, which differ in the presence of tertbutyl pyridine in LP1. An efficiency of 6% under standard measurement conditions has been achieved for 1a þ LP1. However, for porphyrin 1b the use of electrolyte LP1 led to lower efficiencies and a value of approximately 4% was obtained. The differences between the two types of solar cells and the electrolytes have been studied in-depth using photo-induced time-resolved techniques such as CE (Charge Extraction) and TPV (Transient PhotoVoltage).

In this work we study the different electrical loss pathways occurring during the operation of bulk heterojunction solar cells by using a variety of electrical and optical characterization techniques beyond the current density–voltage curve (J–V): Impedance Spectroscopy (IS), Charge Extraction (CE) and Transient Photovoltage (TPV). Two sets of devices are analyzed: the first is based on the donor polymer P3HT, known to provide efficient cells using thick active layers (i.e. 270 nm), and the recently developed PTB7 which offers maximum efficiencies for devices with thinner layers (i.e. 100 nm). Devices fabricated with P3HT:PC60BM are not limited by transport of carriers and large active layer thickness may be used. Importantly, increasing the active layer thickness does not modify the contact selectivity. This is supported by analysis of the diode curve measured in the dark (similar leakage currents) and by capacitance–voltage measurements (similar fullerene content covering the cathode). Under these conditions the current density curve under illumination is mainly defined by the recombination processes taking place in the bulk of the active layer. In contrast, transport of carriers and contact selectivity are both limiting factors for the PTB7:PC60BM system. In this case, best efficiencies are obtained with a low active layer thickness and a high fullerene ratio. Reduced active layer thickness minimizes undesired electrical resistances related to carrier transport through the bulk of the active layer. High fullerene content enhances the amount of fullerene molecules at the cathode leading to decreased leakage currents. Then, the overall device efficiency will be a combination of the recombination kinetics in the bulk of the active layer, undesired resistance to transport of carriers and leakage current present due to low selectivity of the contact. The use of additives has also been explored which enhances charge generation and extraction. Overall, this work provides a comprehensive guide on how to interpret results obtained from some of the most widely used optoelectronic techniques employed to analyse operating devices.