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This article reviews the latest advancements in perovskite solar cell (PSC) components for innovative photovoltaic applications. Perovskite materials have emerged as promising candidates for next-generation solar cells due to their exceptional light-absorbing capabilities and facile fabrication processes. However, limitations in their stability, scalability, and efficiency have hindered their widespread adoption. This review systematically explores recent breakthroughs in PSC components, focusing on absorbed layer engineering, electron and hole transport layers, and interface materials. In particular, it discusses novel perovskite compositions, crystal structures, and manufacturing techniques that enhance stability and scalability. Additionally, the review evaluates strategies to improve charge carrier mobility, reduce recombination, and address environmental considerations. Emphasis is placed on scalable manufacturing methods suitable for large-scale integration into existing infrastructure. This comprehensive review thus provides researchers, engineers, and policymakers with the key information needed to motivate the further advancements required for the transformative integration of PSCs into global energy production.

At present, heavy-metal-free quantum dot light-emitting diodes (QLEDs) have shown great potential as a research hotspot in the field of optoelectronic devices. This article reviews the research on heavy-metal-free quantum dot (QD) materials and light-emitting diode (LED) devices. In the first section, we discussed the hazards of heavy-metal-containing quantum dots (QDs), such as environmental pollution and human health risks. Next, the main representatives of heavy-metal-free QDs were introduced, such as InP, ZnE (E=S, Se and Te), CuInS2, Ag2S, and so on. In the next section, we discussed the synthesis methods of heavy-metal-free QDs, including the hot injection (HI) method, the heat up (HU) method, the cation exchange (CE) method, the successful ionic layer adsorption and reaction (SILAR) method, and so on. Finally, important progress in the development of heavy-metal-free QLEDs was summarized in three aspects (QD emitter layer, hole transport layer, and electron transport layer).

The electron transport layer (ETL) has been extensively investigated as one of the important components to construct high-performance perovskite solar cells (PSCs). Among them, inorganic semiconducting metal oxides such as titanium dioxide (TiO2), and tin oxide (SnO2) present great advantages in both fabrication and efficiency. However, the surface defects and uniformity are still concerns for high performance devices. Here, we demonstrated a bilayer ETL architecture PSC in which the ETL is composed of a chemical-bath-deposition-based TiO2 thin layer and a spin-coating-based SnO2 thin layer. Such a bilayer-structure ETL can not only produce a larger grain size of PSCs, but also provide a higher current density and a reduced hysteresis. Compared to the mono-ETL PCSs with a low efficiency of 16.16%, the bilayer ETL device features a higher efficiency of 17.64%, accomplished with an open-circuit voltage of 1.041 V, short-circuit current density of 22.58 mA/cm2, and a filling factor of 75.0%, respectively. These results highlight the unique potential of TiO2/SnO2 combined bilayer ETL architecture, paving a new way to fabricate high-performance and low-hysteresis PSCs.

Even though Fe2O3 is reported as the electron-transporting layer (ETL) in perovskite solar cells (PSCs), its fabrication and defects limit its performance. Herein, we report a Fe2O3 ETL prepared from FeCl3 solution with a dopant Fe3O4 nanoparticle modification. It is found that the mixed solution can reduce the defects and enhance the performance of Fe2O3 ETL, contributing to improved electron transfer and suppressed charge recombination. Consequently, the best efficiency is improved by more than 118% for the optimized device. The stability efficiency of the Fe2O3-ETL-based device is nearly 200% higher than that of the TiO2-ETL-based device after 7 days measurement under a 300 W Xe lamp. This work provides a facile method to fabricate environmentally friendly, high-quality Fe2O3 ETL for perovskite photovoltaic devices and provides a guide for defect passivation research.

The high performance of perovskite solar cells was produced with the help of an electron transport layer (ETL) and hole transport layer. The film ETL (mesoporous (meso)-TiO2/carbon dot) boosted the efficiency of the perovskite solar cells. A perovskite cell was fabricated by a coating of carbon dot on a meso-TiO2 ETL. The fabricated meso-TiO2/carbon dot-based device has decreased the pin-holes of the perovskite film layer compared to the meso-TiO2-based device, which boosted 3% of the averaged PCE value of the devices. The UV–visible spectroscopy confirmed that the meso-TiO2/carbon dot ETL showed better absorbance, that is, absorbed more incident light than meso-TiO2 ETL to generate higher power conversion efficiency. Coating of carbon dot on meso-TiO2 reduced carrier recombination, and fadeaway of the perovskite film cracks. The X-ray diffraction spectra displayed the removal of the perovskite component after spin-coating of carbon dot to the meso-TiO2 ETL, indicating that the suppression of non-radiative recombination improves the device performance compared to meso-TiO2 ETL. The stability after four weeks on the performance of the device was improved to be 92% by depositing carbon dot on meso-TiO2 ETL compared to the meso-TiO2 ETL-based device (82%). Thus, the high-quality perovskite cell was fabricated by coating carbon dot on a meso-TiO2 ETL, because the electron transport between ETL and perovskite film layer was improved by the injection of electrons from carbon dot.

A hybrid tin-based perovskite solar cell with p-i-n inverted structure is modeled and simulated using SCAPS. The inverted structure is composed of PEDOT:PSS (as hole transport layer—HTL)/GA0.2FA0.78SnI3-1% EDAI2 (as perovskite absorber layer)/C60-fullerene (as electron transport layer—ETL). Previous experimental studies showed that unlike conventional tin-based perovskite solar cells (PSC), the present hybrid tin-based PSC passes all harsh standard tests and generates a power conversion efficiency of only 8.3%. Despite the high stability that this material exhibits, emphasis on enhancing its power conversion efficiency (PCE) is crucial. To that end, various ETL and HTL materials have been rigorously investigated. The impact of energy level alignment between HTL/absorber and absorber/ETL interfaces have been elucidated. Moreover, the thickness and the doping concentration of all the previously mentioned layers have been varied to inspect their effect on the photovoltaic performance of the PSC. The optimized structure with CuI (copper iodide) as HTL and ZnOS (zinc oxysulphide) as ETL scored a PCE of 26%, which is more than three times greater than the efficiency of the initial structure. The current numerical simulation on GA0.2FA0.78SnI3-1% EDAI2 could greatly increase its chance for commercial development.

Recently, the design and fabrication of lead (Pb)-free perovskite or perovskite-like materials have received great interest for the development of perovskite solar cells (PSCs). Manganese (Mn) is a less toxic element, which may be an alternative to Pb. In this work, we explored the role of NH3(CH2)2NH3MnCl4 perovskite as a light absorber layer via SCAPS-1D. A Pb-free PSC device (FTO/TiO2/NH3(CH2)2NH3MnCl4/spiro-OMeTAD/Au) was simulated via SCAPS-1D software. The simulated Pb-free PSCs (FTO/TiO2/NH3(CH2)2NH3MnCl4/spiro-OMeTAD/Au) showed decent power conversion efficiency (PCE) of 20.19%. Further, the impact of the thickness of absorber (NH3(CH2)2NH3MnCl4), electron transport (TiO2), and hole-transport (spiro-OMeTAD) layers were also investigated. Subsequently, various electron transport layers (ETLs) were also introduced to investigate the role of ETL. In further studies, an NH3(CH2)2NH3MnCl4-based PSC device (FTO/TiO2/NH3(CH2)2NH3MnCl4/spiro-OMeTAD/Au) was also developed (humidity = ~30–40%). The fabricated PSCs displayed an open circuit voltage (Voc) of 510 mV with a PCE of 0.12%.

Flexible and printed perovskite solar cells (PSCs) fabricated on lightweight plastic substrates have many excellent potential applications in emerging new technologies including wearable and portable electronics, the internet of things, smart buildings, etc. To fabricate flexible and printed PSCs, all of the functional layers of devices should be processed at low temperatures. Tin oxide is one of the best metal oxide materials to employ as the electron transport layer (ETL) in PSCs. Herein, the synthesis and application of SnO2 quantum dots (QDs) to prepare the ETL of flexible and printed PSCs are demonstrated. SnO2 QDs are synthesized via a solvothermal method and processed to obtain aqueous and printable ETL ink solutions with different QD concentrations. PSCs are fabricated using a slot-die coating method on flexible plastic substrates. The solar cell performance and spectral response of the obtained devices are characterized using a solar simulator and an external quantum efficiency measurement system. The ETLs prepared using 2 wt% SnO2 QD inks are found to produce devices with a high average power conversion efficiency (PCE) along with a 10% PCE for a champion device. The results obtained in this work provide the research community with a method to prepare fully solution-processed SnO2 QD-based inks that are suitable for the deposition of SnO2 ETLs for flexible and printed PSCs.

This work presents the implementation of ultrathin TiO2 films, deposited at room temperature by radio-frequency magnetron sputtering, as electron-selective contacts in silicon heterojunction solar cells. The effect of the working pressure on the properties of the TiO2 layers and its subsequent impact on the main parameters of the device are studied. The material characterization revealed an amorphous structure regardless of the working pressure; a rougher surface; and a blue shift in bandgap in the TiO2 layer deposited at the highest-pressure value of 0.89 Pa. When incorporated as part of the passivated full-area electron contact in silicon heterojunction solar cell, the chemical passivation provided by the intrinsic a-Si:H rapidly deteriorates upon the sputtering of the ultra-thin TiO2 films, although a short anneal is shown to restore much of the passivation lost. The deposition pressure and film thicknesses proved to be critical for the efficiency of the devices. The film thicknesses below 2 nm are necessary to reach open-circuit values above 660 mV, regardless of the deposition pressure. More so, the fill-factor showed a strong dependence on deposition pressure, with the best values obtained for the highest deposition pressure, which we correlated to the porosity of the films. Overall, these results show the potential to fabricate silicon solar cells with a simple implementation of electron-selective TiO2 contact deposited by magnetron sputtering. These results show the potential to fabricate silicon solar cells with a simple implementation of electron-selective TiO2 contact.

The widely used ZnO quantum dots (QDs) as an electron transport layer (ETL) in quantum dot light-emitting diodes (QLEDs) have one drawback. That the balancing of electrons and holes has not been effectively exploited due to the low hole blocking potential difference between the valence band (VB) (6.38 eV) of ZnO ETL and (6.3 eV) of CdSe/ZnS QDs. In this study, ZnO QDs chemically reacted with capping ligands of oleic acid (OA) to decrease the work function of 3.15 eV for ZnO QDs to 2.72~3.08 eV for the ZnO-OA QDs due to the charge transfer from ZnO to OA ligands and improve the efficiency for hole blocking as the VB was increased up to 7.22~7.23 eV. Compared to the QLEDs with a single ZnO QDs ETL, the ZnO-OA/ZnO QDs double ETLs optimize the energy level alignment between ZnO QDs and CdSe/ZnS QDs but also make the surface roughness of ZnO QDs smoother. The optimized glass/ITO/PEDOT:PSS/PVK//CdSe/ZnS//ZnO-OA/ZnO/Ag QLEDs enhances the maximum luminance by 5~9% and current efficiency by 16~35% over the QLEDs with a single ZnO QDs ETL, which can be explained in terms of trap-charge limited current (TCLC) and the Fowler-Nordheim (F-N) tunneling conduction mechanism.

Tin(IV) oxide (SnO2) nanostructures, which possess larger surface areas for transporting electron carriers, have been used as an electron transport layer (ETL) in perovskite solar cells (PSCs). However, the reported power conversion efficiencies (PCEs) of this type of PSCs show a large variation. One of the possible reasons for this phenomenon is the low reproducibility of SnO2 nanostructures if they are prepared by different research groups using various growth methods. This work focuses on the morphological study of SnO2 nanostructures grown by a solvothermal method. The growth parameters including growth pressure, substrate orientation, DI water-to-ethanol ratios, types of seed layer, amount of acetic acid, and growth time have been systematically varied. The SnO2 nanomorphology exhibits a different degree of sensitivity and trends towards each growth factor. A surface treatment is also required for solvothermally grown SnO2 nanomaterials for improving photovoltaic performance of PSCs. The obtained results in this work provide the research community with an insight into the general trend of morphological changes in SnO2 nanostructures influenced by different solvothermal growth parameters. This information can guide the researchers to prepare more reproducible solvothermally grown SnO2 nanomaterials for future application in devices.

Zinc oxide (ZnO) has interesting optoelectronic properties, but suffers from chemical instability when in contact with perovskite interfaces; hence, the perovskite deposited on the top degrades promptly. Surface passivation strategies alleviate this instability issue; however, synthesis to passivate ZnO nanoparticles (NPs) in situ has received less attention. Here, a new synthesis at low temperatures with an ethanolamine post treatment has been developed. By using ZnO NPs prepared with ethanolamine and butanol (BuOH), (E-ZnO), the stability of the FA0.9Cs0.1PbI3 (FACsPI)–ZnO interface was achieved, with a photoconversion efficiency of >18%. Impedance spectroscopy demonstrates that the recombination at the interface was reduced in the system with E-ZnO/perovskite compared to common SnO2/perovskite and that the quality of the perovskite on the top is clearly due to the ZnO in situ passivation with ethanolamine. This work extends the use of E-ZnO as an n-type charge extraction layer and demonstrates its feasibility with methylammonium perovskite. Moreover, this study paves the way for other in situ passivation methods with different target molecules, along with new insights regarding the perovskite interface rearrangement when in contact with the modified electron transport layer (ETL).

Interface modification plays an important role in enhancing the photoelectric conversion efficiency and stability of organic solar cells. In this work, alkali metal lithium chloride (LiCl) was introduced between indium tin oxide and polyethyleneimine ethoxylate (PEIE) to prepare a double-layer electron transport layer. Results show that the introduction of LiCl has dual functions. The first function is that LiCl can enhance conductivity, thereby facilitating charge collection. The second function is that the double-layer electron transport layer based on LiCl can induce the crystallization of active layer, thereby enhancing charge transport. Devices with LiCl/PEIE double layer achieve a high power conversion efficiency (PCE) of 3.84%, which is 21.5% higher than that of pristine devices (the PCE of pristine devices with pure PEIE interface layer is 3.16%).

A robust electron transport layer (ETL) is an essential component in planar-heterojunction perovskite solar cells (PSCs). Herein, a sol-gel-driven ZrSnO4 thin film is synthesized and its optoelectronic properties are systematically investigated. The optimized processing conditions for sol-gel synthesis produce a ZrSnO4 thin film that exhibits high optical transmittance in the UV-Vis-NIR range, a suitable conduction band maximum, and good electrical conductivity, revealing its potential for application in the ETL of planar-heterojunction PSCs. Consequently, the ZrSnO4 ETL-based devices deliver promising power conversion efficiency (PCE) up to 19.05% from CH3NH3PbI3-based planar-heterojunction devices. Furthermore, the optimal ZrSnO4 ETL also contributes to decent long-term stability of the non-encapsulated device for 360 h in an ambient atmosphere (T~25 °C, RH~55%,), suggesting great potential of the sol-gel-driven ZrSnO4 thin film for a robust solution-processed ETL material in high-performance PSCs.

Recently, indium oxide (In2O3) thin films have emerged as a promising electron transport layer (ETL) for perovskite solar cells; however, solution-processed In2O3 ETL suffered from poor morphology, pinholes, and required annealing at high temperatures. This research aims to carry out and prepare pinhole-free, transparent, and highly conductive In2O3 thin films via atomic layer deposition (ALD) seizing efficiently as an ETL. In order to explore the growth-temperature-dependent properties of In2O3 thin film, it was fabricated by ALD using the triethyl indium (Et3In) precursor. The detail of the ALD process at 115–250 °C was studied through the film growth rate, crystal structure, morphology, composition, and optical and electrical properties. The film growth rate increased from 0.009 nm/cycle to 0.088 nm/cycle as the growth temperature rose from 115 °C to 250 °C. The film thickness was highly uniform, and the surface roughness was below 1.6 nm. Our results confirmed that film’s structural, optical and electrical properties directly depend on film growth temperature. Film grown at ≥200 °C exhibited a polycrystalline cubic structure with almost negligible carbon impurities. Finally, the device ALD-In2O3 film deposited at 250 °C exhibited a power conversion efficiency of 10.97% superior to other conditions and general SnO2 ETL.

Tantalum (Ta)-doped titanium oxide (TiO2) thin films are grown by plasma enhanced atomic layer deposition (PEALD), and used as both an electron transport layer and hole blocking compact layer of perovskite solar cells. The metal precursors of tantalum ethoxide and titanium isopropoxide are simultaneously injected into the deposition chamber. The Ta content is controlled by the temperature of the metal precursors. The experimental results show that the Ta incorporation introduces oxygen vacancies defects, accompanied by the reduced crystallinity and optical band gap. The PEALD Ta-doped films show a resistivity three orders of magnitude lower than undoped TiO2, even at a low Ta content (0.8–0.95 at.%). The ultraviolet photoelectron spectroscopy spectra reveal that Ta incorporation leads to a down shift of valance band and conduction positions, and this is helpful for the applications involving band alignment engineering. Finally, the perovskite solar cell with Ta-doped TiO2 electron transport layer demonstrates significantly improved fill factor and conversion efficiency as compared to that with the undoped TiO2 layer.

An environment-friendly inverted indium phosphide red quantum dot light-emitting diode (InP QLED) was fabricated using Mg-doped zinc oxide (ZnMgO) as the electron transport layer (ETL). The effects of ZnMgO ETL on the performance of InP QLED were investigated. X-ray diffraction (XRD) analysis indicated that ZnMgO film has an amorphous structure, which is similar to zinc oxide (ZnO) film. Comparison of morphology between ZnO film and ZnMgO film demonstrated that Mg-doped ZnO film remains a high-quality surface (root mean square roughness: 0.86 nm) as smooth as ZnO film. The optical band gap and ultraviolet photoelectron spectroscopy (UPS) analysis revealed that the conduction band of ZnO shifts to a more matched position with InP quantum dot after Mg-doping, resulting in the decrease in turn-on voltage from 2.51 to 2.32 V. In addition, the ratio of irradiation recombination of QLED increases from 7% to 25% using ZnMgO ETL, which can be attributed to reduction in trap state by introducing Mg ions into ZnO lattices. As a result, ZnMgO is a promising material to enhance the performance of inverted InP QLED. This work suggests that ZnMgO has the potential to improve the performance of QLED, which consists of the ITO/ETL/InP QDs/TCTA/MoO3/Al, and Mg-doping strategy is an efficient route to directionally regulate ZnO conduction bands.

In this study, spatial atomic layer deposition (sALD) is employed to prepare titanium dioxide (TiO2) thin films by using titanium tetraisopropoxide and water as metal and water precursors, respectively. The post-annealing temperature is varied to investigate its effect on the properties of the TiO2 films. The experimental results show that the sALD TiO2 has a similar deposition rate per cycle to other ALD processes using oxygen plasma or ozone oxidant, implying that the growth is limited by titanium tetraisopropoxide steric hindrance. The structure of the as-deposited sALD TiO2 films is amorphous and changes to polycrystalline anatase at the annealing temperature of 450 °C. All the sALD TiO2 films have a low absorption coefficient at the level of 10−3 cm−1 at wavelengths greater than 500 nm. The annealing temperatures of 550 °C are expected to have a high compactness, evaluated by the refractive index and x-ray photoelectron spectrometer measurements. Finally, the 550 °C-annealed sALD TiO2 film with a thickness of ~8 nm is applied to perovskite solar cells as a compact electron transport layer. The significantly enhanced open-circuit voltage and conversion efficiency demonstrate the great potential of the sALD TiO2 compact layer in perovskite solar cell applications.