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Significant progress has been made in the advancement of perovskite solar cells, but their commercialization remains hindered by their lead-based toxicity. Many non-toxic perovskite-based solar cells have demonstrated potential, such as Cs 2 AgBi 0.75 Sb 0.25 Br 6 , but their power conversion efficiency is inadequate. To address this issue, some researchers are focusing on emerging acceptor-donor-acceptor'-donor-acceptor (A-DA'D-A)-type non-fullerene acceptors (NFAs) for Cs 2 AgBi 0.75 Sb 0.25 Br 6 to find effective electron transport layers for high-performance photovoltaic responses with low voltage drops. In this comparative study, four novel A-DA'D-A-type NFAs, BT-LIC, BT-BIC, BT-L4F, and BT-BO-L4F, were used as electron transport layers (ETLs) for the proposed devices, FTO/PEDOT:PSS/Cs 2 AgBi 0.75 Sb 0.25 Br 6 /ETL/Au. Comprehensive simulations were conducted to optimize the devices. The simulations showed that all optimized devices exhibit photovoltaic responses, with the BT-BIC device having the highest power conversion efficiency (13.2%) and the BT-LIC device having the lowest (6.8%). The BT-BIC as an ETL provides fewer interfacial traps and better band alignment, enabling greater open-circuit voltage for efficient photovoltaic responses.

Abstract The optimal interface of a perovskite solar cell promotes efficient charge transport to achieve high power conversion efficiency. Tin(IV) oxide is one of the most well-known electron transport materials for perovskite solar cells. Despite tin(IV) oxide serves low hysteresis, low defect concentration and low fabrication temperature of perovskite solar cells, low conduction band edge of tin(IV) oxide limits built-in potential of the solar cell device. Here, we design an organic-inorganic double electron transporting layer by coating a 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene on tin(IV) oxide to improve the electron transporting properties perovskite solar cells. The organic-inorganic double electron transporting layer improves the interfaces of perovskite/electron transporting layer, leading to enhancement of efficiency and stability of the solar cell devices up to >16% for 200 h. This work demonstrates the feasibility of organic-inorganic double electron transport layer for high performance perovskite solar cells. Highlights • ITIC-SnO 2 double electron transporting layer was designed for perovskite solar cells. • ITIC improved the optoelectronic properties of SnO 2 for electron transport layer. • ITIC-SnO 2 enhanced the efficiency and ambient stability of the solar cells. [ABSTRACT FROM AUTHOR]

Graphical abstract The PCE of the TiO 2 modified device improved 50.46% and shows still more than 83% after 168 h, compared to that of ZnO-based cell which decreased to less than 50%. Highlights • The PSC based on ZnO@TiO 2 NRs as ETL was prepared in ambient air (RH55%). • The PCE of the core-shell device improved 50.46% compared to that of ZnO-based cell. • The PCE of the TiO 2 modified device shows still more than 83% after 168 h. • I atoms of PbI 2 slabs bond with Ti atoms of the TiO 2 surface at PbI 2 /TiO 2 interface. Abstract The serious charge recombination originates from the thermal instability of perovskite/ZnO and the low electron injection efficiency of ZnO. It is the important issue to be improved in ZnO-based perovskite solar cell (PSC). In this paper, the core-shell structure of ZnO@TiO 2 nanorod arrays (NRs) is designed as electron transport layer (ETL) for PSC. A novel synthesis of PSC based on ZnO@TiO 2 NRs in ambient atmosphere was proposed. The photoelectric conversion efficiency (PCE) of the core-shell device is 50.46% higher than that of common ZnO nanorod device. This is due to the improved interface contact between nanorods and perovskite layer, and the suppression of charge recombination. The PCE of the TiO 2 modified device shows still more than 83% after 168 h, compared to that of the pristine one which decreased to less than 50%. This is due to TiO 2 modification which can serve as a buffer layer to avoid direct contact between perovskite films and ZnO NRs, and inhibit s the decomposition of perovskite film on ZnO NRs. Both theoretical calculation and Raman test result show that the interaction between CH 3 NH 3 PbI 3 and TiO 2 is mainly the bonding between I atoms of PbI 2 slabs and Ti atoms of the TiO 2 surface at PbI 2 /TiO 2 interface. The mechanism of carrier transport and recombination in the PSC based on ZnO and ZnO@TiO 2 NRs was also discussed. These results highlight the potential of ZnO@TiO 2 NRs as ETL for all-solid-state PSC with high efficiency and good stability. [ABSTRACT FROM AUTHOR]

Abstract We introduced phenyl-C61-butyric acid methyl ester (PCBM) as an electron transport layer to improve the performance of metal-oxide-free perovskite solar cells (PSCs) using high-conductivity poly(3,4-ethylenedioxylenethiophene):poly(styrene sulfonate) (PEDOT:PSS) as the cathode. The work function of the PEDOT:PSS was tuned from −5.08 to −4.05 eV by using polyethylenimine, improving the electron collection. Using PCBM improved the electron transport and suppressed the charge recombination of the PSCs. The power-conversion efficiency (PCE) of the rigid PSCs (on glass substrates) was significantly improved from 12.5% to 13.9%, and the open-circuit voltage, short-circuit current density, and fill factor were improved simultaneously. The long-term stability of the PSCs was also improved: the PCE degradation of the PSCs without encapsulation decreased from 18.4% to 13.0% after 114 h. Using a 37-nm PCBM layer, the flexible PSCs on polyethylene naphthalate substrates exhibited a high PCE of 11.4% with good bendability. Our results indicate that using PCBM as an electron transport layer in metal-oxide-free PSCs is a feasible method for the large-scale roll-to-roll production of PSCs. Graphical abstract Image 1 Highlights • High-performance metal-oxide-free PSC produced with PCBM as electron transport layer. • High PCE of 13.9% was achieved for rigid PSCs on a glass substrate. • Long term stability of the PSCs was also improved upon using PCBM. • Flexible PSCs on a PEN substrate exhibited a high PCE of 11.4% with good bendability. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Doping of mesoporous TiO 2 layers with Al and Mg to improve PCEs of PSCs. • Al doping eliminates deep trap sites in lattice and decreases band gap of TiO 2. • J SC , V OC , and FF increase in PSCs with Al doped mesoporous TiO 2. • Mg doping increases band gap of TiO 2 ; V OC increases in PSCs with Mg doped TiO 2. Abstract In this work, we investigate how Al and Mg doped mesoporous TiO 2 layers can improve the power conversion efficiency (PCE) of perovskite solar cells (PSCs) with respect to undoped mesoporous TiO 2. The PSC configuration used in this study consists of mesoscopic structure with CH 3 NH 3 PbI 3 as the perovskite absorber. A PSC with optimized mol% of Al and Mg doped mesoporous TiO 2 layers has been shown to achieve up to 22% higher efficiency than that of pure TiO 2. While the Mg doping only enhances the open-circuit voltage (V OC), the Al doping effectively enhances the V OC , the short-circuit current density (J SC), and the fill factor (FF). The occupancy of the doped metals in the lattice is confirmed by XRD, EDX, and XPS. The Mg doping increases the band gap of TiO 2 while the Al doping decreases it. The wide band gap in Mg doped TiO 2 reduces the electron and hole recombination rate, thus increasing the J SC and V OC. By Al doping, deep trap sites in the TiO 2 are eliminated, and this effectively reduces the recombination losses and in turn, increases the J SC. The enhanced electron-hole generation rate attributed to the decrease in the band gap of Al doped TiO 2 also increases the J SC. In addition, there is an enhancement on the electron mobility by the presence of Al metal and this gives an increase in the FF. The results have demonstrated the possibility of improving the PCE of PSCs by fine tuning the band gap of mesoporous TiO 2. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • TiO 2 electron transport layer (ETL) prepared by the different Ti precursors. • Tetrabutyl titanate (TT) and titanium diisopropoxide bis (acetylacetonate) (TDB). • Ti precursors influence the quality of ETL and efficiency of solar cell. • TT is more suitable for preparing high-quality TiO 2 ETL. • Perovskite solar cells based on TT-TiO 2 ETL exhibit better efficiency (17.4%). Abstract Perovskite solar cells (PSCs) have attracted enormous attention because of their superior photovoltaic conversion efficiency and low-cost solution processibility. Electron transport layer (ETL) is essential to the performance of PSCs due to its ability of transporting electrons and blocking holes. Herein, the effect of different Ti precursors, tetrabutyl titanate (TT) and titanium diisopropoxide bis (acetylacetonate) (TDB), on the properties of derived TiO 2 ETL was systematically investigated. It is noted that the change of Ti precursor have significant influence on the surface state and morphology, electron extraction ability and interface recombination resistance, but not on the crystal phases and chemical states of the obtained TiO 2 ETLs. Moreover, compared with TiO 2 ETL derived from TDB, the one obtained from TT displays the superior photoelectric properties and the PSCs based on this ETL acquire the best power conversion efficiency (PCE) of 17.4% with an open-circuit voltage (V oc) of 1.1 V, a short-circuit current density (J sc) of 23.2 mA cm−2 and a fill factor (FF) of 68%. We believe that some fundamental insight into the impact of Ti precursor was provided in this research, aiming to find the criterion of the qualified ETL and paving the route for fabricating desirable ETL. [ABSTRACT FROM AUTHOR]

Abstract The electron-transport layer (ETL) between the PbS colloidal quantum dots (CQDs) active layer and the FTO substrate plays a crucial role in the associated heterojunction photovoltaics. However, the presence of surface defects in the ETL limits the performance of the photovoltaics. Herein, we report the improved carrier extraction at the TiO 2 /PbS interface of planar PbS CQDs photovoltaics, which can be easily accomplished through pre-implanting thermally stable hydroxyl radicals on the surface of TiO 2 nanoparticles (NPs) for constructing ETL. The pre-implantations on the surface of TiO 2 NPs realized using HNO 3 aqueous solution treatment under the hydrothermal condition surprisingly wouldn't be completely removed after the annealing procedure necessary for preparing the conventional ETL, and effectively eliminate the interband trap sites of the TiO 2 NPs by passivating intrinsic oxygen-deficient defects for achieving well-matched electron affinity and work function. As expected, the interfacial bimolecular recombination events are obviously suppressed thanks to the well-acceptable trap densities existing in TiO 2 ETL as well as favorable interfacial band alignment for carrier extraction. Consequently, the power conversion efficiency (PCE) is pushed up to 9.31%, much better than the control competitors. Undoubtedly, this work provides another opportunity for optimizing performance of the relevant PbS CQDs photovoltaics resorting to interface engineering guideline. Graphical abstract fx1 Highlights • Anatase TiO 2 nanoparticles can be easily separated from TiO 2 P25 system. • The hydroxyl radicals implanted on anatase TiO 2 nanoparticles are thermally stable. • The implantations can realize well passivation and favorable band alignment. • The PCE can be pushed up to 9.31% with impressive stability by our strategy. [ABSTRACT FROM AUTHOR]

Abstract Organic-inorganic hybrid perovskites have attracted great attentions for photovoltaic applications due to impressive energy conversion efficiency and low cost fabrication. This article reports the effect of photogenerated dipoles in the electron transport layer (ETL) on the photovoltaic actions in perovskite solar cells (PSCs). A nonfullerene material ITIC with optically induced dipoles was doped into PCBM acting as ETL in inverted planar structure PSCs (ITO/PEDOT:PSS/MAPbI 3-x Cl x /ETL/PEI/Ag). The power conversion efficiency (PCE) of PSCs increases from 13.48% to 14.52% with introducing ITIC into ETL. The capacitance measurements indicate that optically induced dipoles can decrease interfacial charge accumulation. Furthermore, impedance spectroscopy suggests the charge recombination as well as ionic migration are reduced with ITIC doped ETL. Steady and transient PL spectra reveal that the electron extraction is more efficient with optically induced dipoles in the ETL. These results provide unique design of ETL in perovskite solar cells. Graphical abstract Image Highlights • ITIC with optically polarizable molecules was introduced into ETL to enhance the photovoltaic performance of PSCs. • The effect of photogenerated dipoles on photovoltaic actions in PSCs were revealed by impedance spectroscopy and PL spectra. • Our results provide a unique method for improving photovoltaic actions in inverted planar structure PSCs. [ABSTRACT FROM AUTHOR]

Abstract Ruddlesden–Popper type two-dimensional (2D) and quasi-2D perovskite-based photovoltaics have been attracting increasing attention due to their high power conversion efficiency (PCE) and long-term stability. In this work, we fabricated inverted 2D perovskite solar cells (PSCs) using a non-fullerene acceptor as electron transport material. Employing a 55-nm thick 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(5-hexylthienyl)-dithieno[2,3-d:2′,3′-d']-s-indaceno[1,2-b:5,6-b']dithiophene (ITIC-Th) as electron transport layer, an average PCE of 8.4% was achieved for the 2D PSCs, which was comparable to that of 2D PSCs based on phenyl-C61-butyric acid methyl ester (PCBM). However, the long-term stability of the 2D PSCs was improved as the degradation of PCE was reduced from 19.8 to 14.6% following a 15-day duration, which can be attributed to the strong hydrophobic property of the ITIC-Th. The best sample based on the 55-nm thick ITIC-Th exhibited a high PCE of 8.9% with a stable power output and negligible hysteresis, indicating the superior electron transport property of ITIC-Th. Our results demonstrate that ITIC-Th is an effective alternative to PCBM to fabricate highly efficient and stable 2D PSCs. Graphical abstract Image 1 Highlights • Non-fullerene acceptor as electron transport layer for 2D PSC fabrication. • High PCE of 8.9% was achieved for fullerene free 2D PSCs. • Long-term stability of the 2D PSCs was enhanced upon using ITIC-Th. • High-performance with stable power output and negligible hysteresis. [ABSTRACT FROM AUTHOR]

To promote commercialization of perovskite solar cells (PSCs), low-temperature processed electron transport layer (ETL) with high carrier mobility still needs to be further developed. Here, we reported two-dimensional (2D) tin disulfide (SnS2) nanosheets as ETL in PSCs for the first time. The morphologies of the 2D SnS2 material can be easy controlled by the in situ synthesized method on the conductive fluorine-doped tin oxide (FTO) substrate. We achieved a champion power conversion efficiency (PCE) of 13.63%, with the short-circuit current density (JSC) of 23.70 mA/cm2, open-circuit voltage (VOC) of 0.95 V, and fill factor (FF) of 0.61. The high JSC of PSCs results from effective electron collection of the 2D SnS2 nanosheets from perovskite layer and fast electron transport to the FTO. The low VOC and FF are the results of the lower conduction band of 2D SnS2 (4.23 eV) than that of TiO2 (4.0 eV). These results demonstrate that 2D material is a promising candidate for ETL in PSCs. [ABSTRACT FROM AUTHOR]

Abstract Tin dioxide (SnO 2) is regarded as an effective electron transport material for attaining high-performance perovskite solar cells (PSCs). Herein, vertically aligned SnO 2 nanorod arrays are grown directly on fluorine-doped tin oxide (FTO) substrates in an acidic solution via hydrothermal method, where the area density of the nanorod arrays is tailored by varying the precursor concentration. Particularly, the mean diameters of the nanorods increase from 15 to 25 nm and the corresponding area densities decrease from 660 to 460 μm−2 with increasing the concentration of tin(IV) chloride pentahydrate. X-ray diffraction and X-ray photoelectron spectroscopy measurements reveal that the nanorod arrays are pure tetragonal rutile SnO 2 with a high degree of crystallinity. Mixed perovskites of (FAPbI 3) 0.85 (MAPbBr 3) 0.15 are infiltrated into these SnO 2 nanorod arrays, and the perovskite solar cells show an enhanced photovoltaic performance as compared to the nanoparticle counterpart. Perovskite solar cells based on SnO 2 nanorod arrays with the optimized area density exhibit the best power conversion efficiency of 15.46% which is attributed to an accelerated electron transport and a decreased recombination rate at SnO 2 /perovskite interface. Graphical abstract Image 1 Highlights • New approach is exploited for the synthesis of SnO 2 nanorod arrays. • The area density of the nanorod arrays could be tailored. • PSCs using SnO 2 nanorod arrays as ETL yield a high efficiency of 15.46%. • Interfacial charge transfer is systematically investigated. [ABSTRACT FROM AUTHOR]

We fabricated inverted polymer solar cells (PSCs) with the structure of ITO/ZnO NPs/Active layer/MoO3/Ag, in which ZnO NPs act as electron transport layer (ETL), poly{4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b0]-dithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophene-4,6-diy (PTB7) as donor and [6,6]-phenyl-C71-butyric-acidmethyl-ester (PC71BM) as accepter. It is found that the temperature employed during the annealing process of ZnO NPs has significant impact on the efficiency of the resulted PSCs. The optimized PSC with ZnO NPs annealed at 150 °C based on PTB7:PC71BM (1:1.5 w/w) exhibited a power-conversion efficiency of 7.37% with open-circuit voltage (Voc) of 0.722 V, short-circuit current density (Jsc) of 15.38 mA cm−2, and fill factor (FF) of 66.4%. The effects of the annealing temperature on photovoltaic performances were further illustrated with transmission spectrum, atomic force microscopy, X-ray diffraction and PL spectra, meanwhile electrical performance were illustrated with conductivity. Our result indicated that the improved efficiency is due to the optimized ETL/active layer interface, the enhanced transparency and electron transport of the ETLs. As its facile preparation process, this kind of ETL is compatible with roll-to-roll manufacturing of larger area flexible PSCs. [ABSTRACT FROM AUTHOR]

Abstract: Electron selective intermediate layers are crucial for both efficiency and stability of the inverted polymer solar cells (I‐PSCs). In this paper, an established low‐temperature (<130 °C) recipe to fabricate nano zinc oxide (ZnO) layers (L‐ZnO) exhibited typical values of power conversion efficiency (PCE∼3.3%) with the standard P3HT:PC61BM blend. However, PCEs showed further improvement up to ∼24% (∼ 4.08%) when these layers were annealed at 300 °C (H‐ZnO). This annealing step can be bypassed by adopting a slightly different chemistry using Nafion as a modifier (NM‐ZnO). I‐PSCs fabricated with NM‐ZnO showed nearly 40% increase in the PCE (∼4.62%) with PEDOT:PSS hole transport layers (HTL) that matches the so far highest recorded value for such a system. For the low‐bandgap polymer blend PBDTT‐FTTE:PC71BM, a peak efficiency of ∼6.77% was obtained compared to ∼5.34% with L‐ZnO (∼28% increase). Our experiments revealed that these enhancements were due to a combination of benefits obtained from Nafion modification such as favourable positioning of work function (WF), high band gap (Eg) and better transport characteristics through the layer interfaces. [ABSTRACT FROM AUTHOR]

An electron transport layer (ETL) is essential for charge separation and electron extraction in perovskite solar cells (PSCs). In this work, we develop an efficient electron transport layer material SnO 2 -PMo 12 composite for the fully printable hole transport material (HTM)-free PSCs, in which PMo 12 denotes the Keggin-type polyoxometalate H 3 PMo 12 O 40 . Benefitting from the synergistic effect of polyoxometalates, SnO 2 -PMo 12 shows enhanced electron mobility, faster electron extraction and proper downward shift of the conduction band minimum, which boosts the injection and transfer of electrons from the perovskite to the ETL and effectively suppresses charge recombination. In addition, the hysteresis-free behavior appears in the SnO 2 -PMo 12 device, suggesting a remarkable improvement in photovoltaic performance and device stability. Compared to the conventional TiO 2 ETL, the average power conversion efficiency of the device with SnO 2 -PMo 12 ETL is boosted from 10.1% to 12.6%. This work brings a new insight into the promoting photovoltaic performance and stability of the fully printable HTM-free PSCs. [ABSTRACT FROM AUTHOR]

Ternary organic solar cells (OSCs) with the efficiency over 10% are fabricated as an inverted structure with core/shell type quantum dots (QDs) as third component. Förster resonance energy transfer occurs due to overlap between the emission range (λem = 500–800 nm) of InP/ZnS QDs and the absorption range (λabs = 550–800 nm) of PTB7‐Th donor polymer. InP/ZnS QDs increase the photocurrent of the hybrid active layer via the strong emission properties of ZnS shells surrounding the InP core QDs, which transfer photon energy to PTB7‐Th (UV‐vis spectroscopy and photoluminescence). X‐ray photoelectron spectroscopy (XPS) depth profiling reveals that InP/ZnS QDs are distributed on the surface of the hybrid active layer, while grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) analysis reveals that these QDs enhance the crystalline structure of the hybrid active layer. The incorporation of an ethanedithiol (EDT)‐modified ZnO layer as an electron transport layer enhances the carrier transport and decreases carrier recombination, providing a uniform morphology and surface potential favorable for electron extraction and transport, as indicated by atomic force microscopy and electrostatic force microscopy analyses. Due to the synergistic effects of InP/ZnS QDs and the EDT‐modified ZnO layer, the power conversion efficiency (PCE) is 10.2% via the enhancement in short‐circuit current density (JSC) from 17.4 to 18.4 mA cm−2 and fill factor (FF) from 67.2 to 69.3%. [ABSTRACT FROM AUTHOR]

In this study, suspended zinc oxide nanoparticles were used as the electron transport layer in trans-perovskite solar cells. The perovskite film was prepared by a liquid two-step method, and the crystallinity, surface morphology, and optical and photoelectric properties of the perovskite films were then investigated. The results showed that the crystallinity and film compactness of the perovskite could be controlled by the stoichiometric quantity and the perovskite formation rate. Moreover, the film morphology was affected by the annealing temperature, duration, and the amount of toluene solvent, which could be leveraged to enhance the efficiency of the device due to the charge trapping defect. The optimal annealing temperature and duration were 80 °C and 10 min, and the optimal volume ratio of isopropyl alcohol to toluene was 9:1. The highest performing perovskite solar cells in this study exhibited an energy conversion efficiency of 15.78%, a short-circuit current of 20.80 mA/cm 2 , an open circuit voltage of 1.10 V, and a fill factor of 0.69. [ABSTRACT FROM AUTHOR]

Abstract: SnO2 has been well investigated in many successful state‐of‐the‐art perovskite solar cells (PSCs) due to its favorable attributes such as high mobility, wide bandgap, and deep conduction band and valence band. Several independent studies show the performances of PSCs with SnO2 are higher than that with TiO2, especially in device stability. In 2015, the first planar PSCs were reported with a power conversion efficiency over 17% using a low temperature sol‐derived SnO2 nanocrystal electron transport layer (ETL). Since then, many other groups have also reported high performance PSCs based on SnO2 ETLs. SnO2 planar PSCs show currently the highest performance in planar configuration devices (21.6%) and are close to the record holder of TiO2 mesoporous PSCs, suggesting their high potential as ETLs in PSCs. The main concerns with the application of SnO2 as ETL are that it suffers from degradation in high temperature processes and that its much lower conduction band compared to perovskite may result in a voltage loss of PSCs. Here, notable achievements to date are outlined, the unique attributes of SnO2 as ETLs in PSCs are described, and the challenges facing the successful development of PSCs and approaches to the problems are discussed. [ABSTRACT FROM AUTHOR]

Oxygen-related defects in the intrinsic metal-oxide films restrict the transportation and collection processes of photogenerated carriers from the perovskite film to charge transport layers, which obstruct the applications of metal-oxide films in perovskite solar cells (PSCs). In this study, fluorine as an anion dopant was introduced to modify the oxygen-related defects in the intrinsic zinc oxide (ZnO). The impact of fluorine concentration on the structural, electrical, and optical characteristics of solution-processed ZnO films was systematically investigated. When the fluorine concentration was optimized to 15%, fluorine-doped ZnO (ZnO:F) film exhibited multiple advantageous effects, such as large crystalline size, low oxygen-related defect state density, good hydrophobic surface, and high conductivity. Furthermore, ZnO:F films with various fluorine concentrations as electron transport layers (ETLs) were introduced into the PSCs. The PSCs based on the ZnO:F ETL with the fluorine concentration of 15% yielded a maximum power conversion efficiency of 16.23% owing to the improvements of short-circuit current and fill factor. Meanwhile, the thermochemical stability of the device based on the ZnO:F ETL was also significantly improved. [ABSTRACT FROM AUTHOR]

The exceptional electrical properties of the graphene offer many opportunities for the performance improvement in the devices. In this study, the importance of incorporation of solution processed graphene as an electron transport layer (ETL) in bulk heterojunction (BHJ) devices is elucidated by measuring the current-voltage characteristics under dark and illumination conditions. Raman spectra P3HT:PCBM blend thin films display the same modes as of pristine P3HT. The UV/Vis analysis confirms the formation of P3HT:PCBM blend. The three different devices of architectures: standard structure, standard structure with ETL and inverted structure with ETL, comprising active layer of as-prepared P3HT:PCBM blends are fabricated and compared. Various Schottky diode parameters like ideality factor, series resistance, and barrier height are determined from current-voltage curves using Cheung and Cheung approach. The incorporation of graphene ETL in the device shows the enhancement in photocurrent resulting from the better extraction and improved charge collection efficiency. The photovoltaic effect is also observed for inverted device configuration. The charge transport analysis of the devices show overall power law trend, i.e. Ohmic current at low voltage followed by space charge limited conduction in existence of discrete trap levels at higher voltage range. [ABSTRACT FROM AUTHOR]

We present new architectures in CH 3 NH 3 PbI 3 based planar perovskite solar cells incorporating solution processed SnO 2 /MgO composite electron transport layers that show the highest power outputs ever reported for photovoltaic cells under typical 200–400 lx indoor illumination conditions. When measured under white OSRAM LED lamp (200, 400 lx), the maximum power density values were 20.2 µW/cm 2 (estimated power conversion efficiency, PCE = 25.0%) at 200 lx and 41.6 µW/cm 2 (PCE = 26.9%) at 400 lx which correspond to a ∼ 20% increment compared to solar cells with a SnO 2 layer only (even at standard 1 sun illumination, where the maximum PCE was 19.0%). The thin MgO overlayer leads to more uniform films, reduces interfacial carrier recombination, and leads to better stability. All layers of the cells, except for the two electrodes, are solution processed at low temperatures for low cost processing. Furthermore, ambient indoor conditions represent a milder environment compared to stringent outdoor conditions for a technology that is still looking for a commercial outlet also due to stability concerns. The unparalleled performance here demonstrated, paves the way for perovskite solar cells to contribute strongly to the powering of the indoor electronics of the future (e.g. smart autonomous indoor wireless sensor networks, internet of things etc). [ABSTRACT FROM AUTHOR]

This paper presents the surface morphological, optical and charge transport characterization of thermally evaporated thin film of organic material, namely 3, 5-Bis (4-tert-butylphenyl)-4-phenyl-4H-1, 2, 4-triazole (abbreviated as BBPT) prepared by well-known thermal evaporation technique, to be applied as an electron transport material in optoelectronic devices. Carrier mobility and AC conductivity are estimated from frequency dependent admittance -5 characterization performed over a single layer device having structure ITO/ BBPT /Al and are found in the range 5.17 x 10-5 cm2 V1 s-1 and 4.83575 × 10 ohm m, respectively. Various electrical parameters are calculated from charge transport characterization of ITO/ BBPT /Al device. Results of this work demonstrated that the conduction mechanism is in good correlation with the theory of hopping conduction in amorphous materials and the material studied have a potential application as an Electron Transport Layer (ETL) material in optoelectronic devices. [ABSTRACT FROM AUTHOR]

Interface engineering that involves in the metal cathodes and the electron transport layers (ETLs) facilitates the simultaneous improvement of device performances and stability in perovskite solar cells (PSCs). Herein, low-temperature solution-processed cerium oxide (CeO x ) films are prepared by a facile sol-gel method and employed as the interface layers between [6,6]-phenyl-C 61 -butyric acid methyl ester (PC 61 BM) and an Ag back contact to form PC 61 BM/CeO x double ETLs. The introduction of CeO x enables electron extraction to the Ag electrode and protects the underlying perovskite layer and thus improves the device performance and stability of the p-i-n PSCs. The p-i-n PSCs with double PC 61 BM/CeO x ETLs demonstrate a maximum power conversion efficiency (PCE) of 17.35%, which is superior to those of the devices with either PC 61 BM or CeO x single ETLs. Moreover, PC 61 BM/CeO x devices exhibit excellent stability in light soaking, which is mainly due to the chemically stable CeO x interlayer. The results indicate that CeO x is a promising interface modification layer for stable high-efficiency PSCs. [ABSTRACT FROM AUTHOR]

Abstract: Adopting proper electron transport layers (ETLs) is essential to high‐performance all‐inorganic perovskite light‐emitting diodes (PeLEDs). However, the effect of ETLs has not been comprehensively investigated in all‐inorganic nanocrystal PeLEDs, while 2,2′,2′′‐(1,3,5‐benzenetriyl) tris‐[1‐phenyl‐1H‐benzimidazole] (TPBi) is the most common ETL. Herein, a novel strategy is proposed to enhance the efficiency of nanocrystal PeLEDs. Tris(8‐hydroxyquinoline) aluminum (Alq3) is incorporated into TPBi to form a new ETL TPBi/Alq3/TPBi, simultaneously enabling charge balance and confinement. The green PeLED with new ETL exhibits a maximum external quantum efficiency (EQE) of 1.43%, current efficiency of 4.69 cd A−1, and power efficiency of 1.84 lm W−1, which are 191%, 192%, and 211% higher than those of PeLEDs with conventional ETL TPBi, respectively. Significantly, the EQE is 36‐fold higher than that of PeLED with high electron mobility ETL. Impressively, the full width at half‐maximum of electroluminescence emission is 16 nm, which is the narrowest among CsPbBr3 PeLEDs. The findings may present a rational strategy to enhance the device engineering of all‐inorganic PeLEDs. [ABSTRACT FROM AUTHOR]

SnO 2 with its excellent properties such as high optical transparency, suitable band energy and high electron mobility, recently has received special attention from researchers as an outstanding electron transport layer (ETL) for optoelectronic devices. Here, we demonstrate that SnO 2 combined with ionic liquid (IL), 1-benzyl-3-methylimidazolium chloride ([BzMIM]Cl), based on low-temperature solution-processed can be an excellent ETL for efficient inverted organic solar cells (iOSCs). Our best performance with P3HT:PC 60 BM based iOSCs using SnO 2 /IL as an ETL, has achieved a power conversion efficiency (PCE) of 4.05%, which is the highest reported value so far and was a 38% increase compared to that of SnO 2 only (2.94%). Using ultraviolet photoelectron spectroscopy, we found that the work function of the cathode decreased significantly from − 4.38 eV to − 3.82 eV for SnO 2 /IL, an outstanding feature that is necessary for an ideal ETL. Electrochemical impedance spectroscopy studies revealed a significant lower transport resistance and an efficient charge extraction at the interface between photoactive layer and the electrode for the SnO 2 /IL-based iOSC than for the SnO 2 only device. The iOSC devices using SnO 2 /IL showed excellent long-term stability, with a PCE of ~ 81% compared to the initial value after storage for 2.5 months in ambient conditions. This low-temperature solution-processed SnO 2 /IL is expected for low-cost, high throughput, roll-to-roll process on flexible substrates for iOSC as well as other optoelectronic devices. [ABSTRACT FROM AUTHOR]

The breakthrough discovery of organic-inorganic hybrid perovskite materials for converting solar energy into electrical energy has revolutionized the third generation photovoltaic devices. Within less than half a decade of rigorous research and development in perovskite solar cells, the efficiency is boosted upto 22%. Aforesaid high PCE is accredited to high optical absorption properties, balanced charge transport properties, and longer diffusion lengths of carriers. Two dominant perovskite solar cell architecture has evolved; n-i-p, and p-i-n with mesoporous or planar heterojunction. In planar heterojunction configuration, perovskite light harvester is layered between hole/electron transport layers and the electrodes. The electron and hole transporting films increase charge collection efficiency and reduce recombination at interfaces. In the following review, we present a critical survey of the recent progress in perovskite absorber and charge transport materials that account for the exceptionally higher PCE of perovskite devices. Furthermore, numerous fabrication techniques and device architectures are summarized. [ABSTRACT FROM AUTHOR]

In this letter, high-performance TiO 2 /BiFeO 3 heterostructure thin film is successfully prepared by introducing sol-gel derived-TiO 2 (SG-TiO 2 ) electron transport layer. A significant improvement of photovoltaic performance has been achieved. 3.674% power conversion efficiency of the thin film is obtained with open-circuit voltage (V oc ) of 1.64 V, short-circuit photocurrent (J sc ) of 3.5 mA/cm 2 and fill factor (FF) of 64%, which implies that the introduction of a TiO 2 would improve the photovoltaic performance under visible light illumination. Our work demonstrates that the TiO 2 /BFO heterostructure thin film possesses the potential for better use in the solar energy devices applications. [ABSTRACT FROM AUTHOR]

In planar perovskite solar cells (PSCs), the electron transport layer (ETL), with the function of transporting electrons and blocking holes, plays a significant role in determining the photoelectric conversion properties. Thus, it is crucial to exploit potential ETL materials for improved performance. Herein, we demonstrate efficient planar PSCs employing ultrathin Nb 2 O 5 films as ETLs fabricated by a facile spin-coating method. The effects of the precursor concentration and annealing time of Nb 2 O 5 on the photovoltaic performance are investigated in detail. The planar PSCs constructed with 0.02 M-prepared Nb 2 O 5 films sintered for 1 h possess an optimized performance, giving rise to a champion efficiency of 14.82% with high reproducibility. The superior performance is ascribed to the appropriate conduction band position of Nb 2 O 5 , high transmittance, increased charge transport, and diminished charge recombination of the Nb 2 O 5 film. The results demonstrate that the utilization of spin-coated Nb 2 O 5 as the ETL provides a new platform to construct highly-efficient planar PSCs. [ABSTRACT FROM AUTHOR]

To modify the stoichiometry and enhance electronic transportation of electron transport layers (ETLs) potentially for the large-scale high performance planar perovskite solar cells (PSCs) on the flexible substrate, ZnO films as ETLs with controlled stoichiometry are fabricated by magnetron sputtering method under a mixture working gases of Ar and O 2 at room temperature. The impact of Ar/O 2 ratios on the structural, electrical, and optical properties of ZnO films is systematically investigated. The X-ray photoelectron spectroscopy results indicate that the sputtered ZnO films with controlled stoichiometry are successfully achieved. For the proper deposition condition with Ar/O 2 ratio of 1:4, ZnO film exhibits large-size grains, low defect states density, and good optical crystalline quality. Furthermore, the sputtered ZnO films deposited under various Ar/O 2 ratios are introduced into the PSCs as ETLs. The photovoltaic performance of the PSCs is strongly dependent on the properties of the sputtered ZnO ETLs. Compared with the ZnO ETLs prepared under various Ar/O 2 ratios, the PSCs based on the ZnO ETL deposited under the Ar/O 2 ratio of 1:4 demonstrate the improved short-circuit current and fill factor, contributing to a maximum power conversion efficiency of 16.60%. This study highlights that the sputtered ZnO film is one of promising ETLs for high-efficiency PSCs under low-temperature processing. [ABSTRACT FROM AUTHOR]

We fabricated inverted perovskite solar cells (PSCs) using different organic solvents, including chloroform, chlorobenzene, and 1,2-dichlorobenzene, to prepare the phenyl-C61-butyric acid methyl ester (PCBM) layer. We found that using 1,2-dichlorobenzene resulted in smoother PCBM morphology compared to the chloroform- and chlorobenzene-based solvents; this would be beneficial for improving charge transport between the perovskite and cathode. In accordance with the morphologies, the average power conversion efficiency (PCE) of 1,2-dichlorobenzene-processed PSCs was 17.5%, which was higher than those of chlorobenzene- and chloroform-processed PSCs (16.7% and 11.0%, respectively) The best-performing cell was fabricated using 1,2-dichlorobenzene, showing PCEs of 17.9% and 18.2% in forward and reverse scans, respectively. We found that the conductivity and the PCBM surface roughness showed good linear dependence on the evaporation rate of the solvent, which could be an important factor for identifying new good organic solvents. [ABSTRACT FROM AUTHOR]

In this study we present a ternary alloy, Cd1−xZnxS as an electron transport layer for a planar lead halide perovskite solar cell via numerical simulation with solar cell capacitance simulator (SCAPS) software. Performance dependence on molar composition variation in the Cd1−xZnxS alloy was studied for the mixed perovskite CH3NH3PbI3−xClx absorber and spiro-OMeTAD hole transport material in a planar perovskite solar cell. Additionally, the defects on both Cd1−xZnxS/CH3NH3PbI3−xClx and CH3NH3PbI3−xClx/spiro-OMeTAD interface were thoroughly investigated. Simultaneously, a thickness of 700 nm for CH3NH3PbI3−xClx absorber with 50-nm-thick Cd0.2Zn0.8S (x = 0.8) was optimized. Analysis of the numerical solutions via SCAPS provides a trend and pattern for Cd0.2Zn0.8S as an effective electron transport layer for planar perovskite solar cells with a yield efficiency up to 24.83%. The planar perovskite solar cell shows an open-circuit voltage of 1.224 V, short-circuit current density of 25.283 mA/cm2 and a fill factor of 80.22. [ABSTRACT FROM AUTHOR]

Displays made using colloidal quantum dots as electroluminescent (EL) emitter is a very promising display technology because it is efficient, emits pure color, and is inexpensive. We have demonstrated highly efficient red, green, and blue quantum dot light emitting diodes (QLEDs) using a colloidal zinc oxide nanoparticle electron transport layer. Here, we will report QLEDs with external quantum efficiency >15% for red, green, and blue color (approaching the theoretical‐limit of ~22% for green) QLEDs. Finally, we will discuss some of the challenges that must be addressed to successfully commercialize EL‐QLED displays. [ABSTRACT FROM AUTHOR]

In this study, we investigated methylammonium lead iodide (MAPbI3)-perovskite solar cells (PSCs) with hybrid PC70BM/ZnO interlayers. The pristine device which had a PC70BM electron transport layer sandwiched between ITO/PEDOT:PSS/MAPbI3 and TiOx/Al electrodes exhibited PCE of 12.72% with a VOC of 0.98 V, Jsc of 18.41 mA/cm2, and FF of 71%. The new device with hybrid PC70BM/ZnO interlayers exhibited higher PCE of 14.17% with a VOC of 0.98 V, JSC of 20.08 mA/cm2, and FF of 72% due to the incorporation of ZnO nanoparticles in PC70BM electron transport layer (ETL) with high electron mobility and cascade band gap alignment. Here, we demonstrated that lower photoluminescence (PL) intensity of the device with hybrid interlayers could improve the JSC value of perovskite solar cells due to enhanced charge-generation efficiency. Contact resistance can be reduced by mixing ZnO nanoparticles with PC70BM electron transport layer without additional ZnO layer insertion. [ABSTRACT FROM AUTHOR]

Abstract: Mesoporous titania (TiO2) nanoparticles (NPs) were synthesized by treating prehydrolyzed titanium precursors with polyethylene glycol (PEG). By varying the amount of PEG, their different physical properties were tuned appropriately in terms of surface area, pore size/volume, and electrical conductivity. By increasing the amount of PEG in TiO2, the surface area and pore volume of mesoporous TiO2 increased, and no direct correlation with the photovoltaic performance of perovskite solar cells was observed. In comparison, the pore size of mesoporous TiO2 first increased greatly before quickly decreasing, and a similar trend was also observed for electrical conductivity. These implied that the interparticle interaction became much stronger with an optimum amount of PEG added to form mesoporous TiO2 NPs. With an optimum molar ratio of PEG/Ti precursor at 0.75, greatly improved conductivity of mesoporous TiO2 NPs with interconnection as compared to that prepared in the absence of PEG, which was used as an electron transport layer, improved the power conversion efficiency of perovskite solar cells by ≈36%. Their greatly reduced photoluminescence after incorporating the perovskite also revealed a difference in the electron‐injection properties from the perovskite into mesoporous TiO2. This strategy highlights a versatile tool to tune mesoporous structures to achieve a cooperative effect for studying photovoltaic properties in perovskite solar cells. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract We investigate an electron transport bilayer fabricated at <110 °C to form all low-temperature processed, thermally stable, efficient perovskite solar cells with negligible hysteresis. The components of the bilayer create a symbiosis that results in improved devices compared with either of the components being used in isolation. A sol-gel derived ZnO layer facilitates improved energy level alignment and enhanced charge carrier extraction and a [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) layer to reduce hysteresis and enhance perovskite thermal stability. The creation of a bilayer structure allows materials that are inherently unsuitable to be in contact with the perovskite active layer to be used in efficient devices through simple surface modification strategies. [ABSTRACT FROM AUTHOR]

The rapid development of organometal halide perovskite solar cells (PSCs) has led to reports of power conversion efficiencies of over 22%. TiO 2 is the most commonly used material for the electron transport layer in PSCs. ZnO is an excellent inorganic semiconductor material owing to its large surface area, easy synthesis, direct electron pathways, large variety of synthesizable nanostructures, and low cost of fabrication. It can potentially replace TiO 2 as the electron transport layer material in high efficiency perovskite solar cells based on flexible substrates. However, the number of reported high performance PSCs using ZnO nanostructures is still limited. This review focuses on the recent developments in the application of ZnO nanostructures in PSCs. The current state-of-the-art techniques and the open questions in the area of ZnO-based PSCs are also highlighted. Finally, we present a brief analysis on the opportunities and challenges for the use of ZnO in PSCs. [ABSTRACT FROM AUTHOR]

A set of various perovskite precursor formulations was investigated to elucidate correlations between precursor composition and the crystal structure, film morphology as well as photovoltaic activity of H 3 CNH 3 PbI 3-x Cl x perovskite solar cells. Three precursor solutions in dimethylfromamide (DMF) with defined ratios of lead(II) halide (PbI 2 and/or PbCl 2 ) and methylammonium halide (H 3 CNH 3 I (MAI) and H 3 CNH 3 Cl (MACl)) such as 1:3 (PbCl 2 :MAI), 1:1:4 (PbI 2 :PbCl 2 :MAI) and 1:1:1 (PbI 2 :MAI:MACl) were used to prepare solar cells in primarily ambient atmosphere. Processing the 1:3 (PbCl 2 :MAI) solution in ambient atmosphere yielded perovskite films with rather non-uniform morphology and devices with moderate performance. Perovskite thin films prepared from the 1:1:4 (PbI 2 :PbCl 2 :MAI) and 1:1:1 (PbI 2 :MAI:MACl) formulation showed nearly identical features, high crystallinity, large and compact micrometer-sized crystal domains, and good photovoltaic performance. This indicates that the overall ionic composition in the precursor solution is crucial for the perovskite formation, the source of these ions, however, appears nonrelevant. Furthermore, the effect of different electron transport layers (ETL), PCBM, bis -PCBM, and N -[4-(benzothiadiazol-4-yl)phenyl]- N ′-(1-nonyldecyl)perylene-3,4,9,10-tetracarboxdimide (a-PTCDI) on the photovoltaic performance was analyzed. The highest hysteresis-free power conversion efficiency (PCE) was achieved with PCBM (12.8%) followed by a-PTCDI (8.4%) and bis -PCBM (6%). The degradation of MAPbI 3-x Cl x based devices stored in nitrogen atmosphere was primarily revealed by a loss in fill factor. [ABSTRACT FROM AUTHOR]

The charge transfer and separation are significantly affected by the electron properties of the interface between the electron-donor layer and the carrier-transporting layer in polymer solar cells (PSCs). In this study, we investigate the electron extraction mechanism of PSCs with a low temperature solution-processed ZnO/PEI as electron transport layer. The incorporation of PEI layer can decrease the work function of ZnO and reduce interfacial barrier, which facilitates electron extraction and suppresses bimolecular recombination, leading to a significant performance enhancement. Furthermore, PEI layer can induce phase separation and passivite inorganic surface trap states as well as shift the interfacial energy offset between metal oxide and organic materials. This work offers a simple and effective way to improve the charge transporting property of organic photovoltaic devices. [ABSTRACT FROM AUTHOR]

In the present article, the detailed analyses of interface properties and device performance of inorganic perovskite CaMnO 3 -based buffer layer hybrid perovskite solar cell have been undertaken. Analyses are based on ab initio simulations and macroscopic modelling. A thorough study of electronic and optical properties and interface charge dynamics revealed that CaMnO 3 presents a better candidate for the electron transport material in thin film hole transporting material free hybrid perovskite solar cells with the planar architecture than the most common anatase TiO 2 . This result is founded on the more appropriate band gap and better band alignment with the hybrid perovskite, leading to the faster charge carrier mobility, improved charge transfer and reduced exciton recombination. The results from theoretical simulations are justified by the solar cell model, which explored the basic cell characteristics and parameters: open circuit voltage, short circuit current, fill factor and efficiency, as the functions of cell performance factors, like defect density, diffusion length, absorber layer thickness and band offset. Our model suggests an unoptimized device with a photo-conversion efficiency of almost 10% for the low defect concentrations under 10 15 . With efficiency in the upper range for HTM free perovskite solar cells, we propose that the CaMnO 3 -based solar cell poses as an improvement upon the up to now most frequently used ones and provides important step toward their commercialisation. [ABSTRACT FROM AUTHOR]

The aqueous-based Zn-ammine complex solutions represent one of the most promising routes to obtain the ZnO electron transport layer (ETL) at a low temperature in inverted organic solar cells (OSCs). However, to dope the ZnO film processed from the Zn-ammine complex solutions is difficult since the introduction of metal ions into the Zn-ammine complex is a nontrivial process as ammonium hydroxide tends to precipitate metal salts due to acid-base neutralization reactions. In this paper, we investigate the inverted OSCs with Al-doped-ZnO ETL made by immersion of metallic Al into the Zn-ammine precursor solution. The effects of ZnO layer with different immersion time of Al on film properties and solar cell performance have been studied. The results show that, with the Al-doped-ZnO ETL, an improvement of the device performance could be obtained compared with the device with the un-doped ZnO ETL. The improved device performance is attributed to the enhancement of charge carrier mobility leading to a decreased charge carrier recombination and improved charge collection efficiency. The fabricated thin film transistors with the same ZnO or AZO films confirm the improved electrical characteristics of the Al doped ZnO film. [ABSTRACT FROM AUTHOR]

Atomic layer deposition (ALD) was used to synthesize titanium oxide (TiO) film as an electron transport layer (ETL) in inverted organic photovoltaic cells (IOPVs). By adjusting the ALD precursor ratio and deposition temperature, the thickness of the TiO film was 5 nm, and its effect on the photovoltaic performances was evaluated. We also investigated the effect of nitrogen doping of TiO on the power conversion efficiency (PCE) of the cells. An IOPV cell fabricated with a 0.6%-nitrogen-doped TiO (N-TiO A) ETL exhibited a PCE of 2.27%, which is a 6% increase compared with an equivalent cell containing an undoped TiO ETL. Furthermore, the XPS results confirmed the doping of nitrogen into the samples. The doping improved the electrical properties of the TiO films evidenced by the Hall measurements in terms of conductivity, hall electron mobility and carrier density. [ABSTRACT FROM AUTHOR]

Since perovskite solar cells appeared in 2009, its simple preparation process, high photoelectric conversion efficiency and the characteristic of low cost in preparation process let it become the hot spot of both at-home and abroad. Owing to the constant efforts of scientists, the conversion efficiency of perovskite solar cells is more than 20% now. Perovskite solar cells are mainly composed of conductive glass, electron transport layer and hole transport layer, perovskite layer and electrode parts. This paper will briefly introduce the working principle and working process about the electron transport layer of perovskite solar cells. The paper focuses on aspects such as material types (e.g., inorganic electron transport materials, organic small molecule electron transport materials, surface modified electron transport materials and doped electron transport materials), preparation technology of electron transport layer, the effects of electron transport layer on the photovoltaic performance of the devices, and the electron transport layer in the future research. [ABSTRACT FROM AUTHOR]