Properties of Perovskite Solar Cells with Low Temperature Sintered SnO2 Electron Transport Layers

Influence of Charge Transport Layers on Capacitance Measured in Halide Perovskite Solar Cells

Carrier Dynamics Engineering for High-Performance Electron-Transport-Layer-free Perovskite Photovoltaics

In this study, we improved the photovoltaic (PV) properties and storage stabilities of inverted perovskite solar cells (PVSCs) based on methylammonium lead iodide (MAPbI3) by employing bathocuproine (BCP)/poly(methyl methacrylate) (PMMA) and BCP/polyvinylpyrrolidone (PVP) as hole-blocking and electron-transporting interfacial layers. The architecture of the PVSCs was indium tin oxide/poly(3,4-ethylenedioxythiophene):polystyrenesulfonate/MAPbI3/[6,6]-phenyl-C61-butyric acid methyl ester/BCP based interfacial layer/Ag. The presence of PMMA and PVP affected the morphological stability of the BCP and MAPbI3 layers. The storage-stability of the BCP/PMMA-based PVSCs was enhanced significantly relative to that of the corresponding unmodified BCP-based PVSC. Moreover, the PV performance of the BCP/PVP-based PVSCs was enhanced when compared with that of the unmodified BCP-based PVSC. Thus, incorporating hydrophobic polymers into BCP-based hole-blocking/electron-transporting interfacial layers can improve the PV performance and storage stability of PVSCs.

Incorporating chlorine into the SnO2 electron transport layer (ETL) has proven effective in enhancing the interfacial contact between SnO2 and perovskite in perovskite solar cells (PSCs). However, previous studies have primarily focused on the role of chlorine in passivating surface trap defects in SnO2, without considering its influence on the buried interface. Here, hydrochloric acid (HCl) is introduced as a chlorine source into commercial SnO2 to form Cl-capped SnO2 (Cl-SnO2) ETL, aiming to optimize the buried interface of the PSC. The incorporation of HCl into the SnO2 precursor solution works in two key ways. First, it converts the detrimental KOH stabilizer into KCl through an acid-base reaction. Second, it regulates the crystallization process of the perovskite, reducing PbI2 residues and voids at the buried interface. As a result, the efficiency of the PSC increases from 21.93% to 25.39%, with a certified efficiency of 25.69%, the highest efficiency reported for Cl-SnO2 ETL-based PSCs. Moreover, the target PSC exhibits excellent air stability, retaining 90% of its initial efficiency after 2900h of air exposure, compared to only 56.1% for the control PSC. This investigation highlights the effectiveness of HCl in the synergistic optimization of the buried interface in PSCs.

Properties of electron transporting layer (ETL) play an important role on photovoltaic performances of perovskite solar cells. In this work, effects of Sn incorporation on properties of ZnO-based perovskite solar cells were investigated. Sn-doped ZnO (TZO) thin film as ETL was prepared via a sol–gel method. With 5% atom doping, TZO film coated on an indium doped tin oxide (ITO) substrate provided comparable light transmittance with that of an undoped ZnO/ITO substrate. It was also found that the optical band gap of TZO film (3.30 eV) is slightly wider than that of the ZnO one (3.28 eV). These results suggest that Sn atoms probably incorporated into the ZnO crystal during the sol-gel method. The grains size of perovskite layer coated on TZO or ZnO films also showed variation. The perovskite crystal on the TZO thin film (average 300 nm) was larger than that of the one on ZnO thin film (average 277 nm). The preliminary results indicate that the perovskite solar cell based on TZO film provided higher power conversion efficiency (PCE) of 4.42 % than the ZnO-based device (3.16%). Short-circuit current density (Jsc), open-circuit voltage (Voc) and fill factor (FF) of TZO-based device were also higher than the ZnO-based device. This may be because TZO film may provide lower resistivity and better ETL/perovskite interface contact, confirmed by lower series resistance and higher shunt resistance of the TZO-based device. Finally, this work introduced a simple method to prepare TZO film at low temperature for photovoltaic application. It may help guide the development of flexible solar cells and other optoelectronic devices.

SnO2 film is one of the most widely used electron transport layers (ETL) in perovskite solar cells (PSCs). However, the inherent surface defect states in SnO2 film and mismatch of the energy level alignment with perovskite limit the photovoltaic performance of PSCs. It is of great interesting to modify SnO2 ETL with additive, aiming to decrease the surface defect states and obtain well aligned energy level with perovskite. In this paper, anhydrous copper chloride (CuCl2) was employed to modify the SnO2 ETL. It is found that the adding of a small amount of CuCl2 into the SnO2 ETL can improve the proportion of Sn4+ in SnO2, passivate oxygen vacancies at the surface of SnO2 nanocrystals, improve the hydrophobicity and conductivity of ETL, and obtain a good energy level alignment with perovskite. As a result, both the photoelectric conversion efficiency (PCE) and stability of the PSCs based on SnO2 ETLs modified with CuCl2 (SnO2-CuCl2) is improved in comparison with that of the PSCs on pristine SnO2 ETLs. The optimal PSC based on SnO2-CuCl2 ETL exhibits a much higher PCE of 20.31% as compared to the control device (18.15%). The unencapsulated PSCs with CuCl2 modification maintain 89.3% of their initial PCE after exposing for 16 d under ambient conditions with a relative humidity of 35%. Cu(NO3)2 was also employed to modify the SnO2 ETL and achieved a similar effect as that of CuCl2, indicating that the cation Cu2+ plays the main role in SnO2 ETL modification.

SnO2 electron transport layer (ETL) morphology plays a vital role in carrier transportation and the properties of perovskite solar cells (PSCs). However, the uneven and pore surface would inevitably lead to high interface defects, high hysteresis, and poor performance. In this work, we use a molecular modifier 4-guanidinobenzoic acid methanesulfonate (GAMSA) to build a molecular bridge on the buried interface of SnO2/perovskite. XPS results demonstrate that the ratio of lattice oxygen (OL)/adsorbed oxygen (OV) increased from 1.35 to 2.34 after GAMSA modification, thus, Sn4+ and O vacancy defects in SnO2 were effectively reduced. Meanwhile, the conduction band minimum of the ETL enhanced from -4.33 eV to -4.07 eV, which obviously facilitated the electron transport. As a result, the optimal device exhibits an enhanced efficiency of 22.42%, which is much higher than that of the control one of 20.13%, with a greatly decreased hysteresis index from 14.35% to 3.27%. Notably, the optimized target device demonstrated excellent long-term stability, maintaining an initial efficiency of 87% after 2000 h storage in a N2 atmosphere in the dark at room temperature. This work paves a new method of ETL modification to improve lattice oxygen of SnO2 and restrain hysteresis for the enhanced performance of PSCs.

Charge extraction by electron transport layers (ETLs) plays a vital role in improving the performance of perovskite solar cells (PSCs). Here, PSCs with four different types of ETLs, such as SnO2, amorphous‐Zn2SnO4 (am‐ZTO), am‐ZTO/SnO2, and SnO2/am‐ZTO, are successfully synthesized. The interface recombination behavior and the charge transport properties of the devices affected by four types of ETLs are systematically investigated. For dual am‐ZTO/SnO2 ETLs, compact am‐ZTO ETL prepared by the pulsed laser deposition method provides a dense physical contact with FTO than the spin coating films, decreasing leakage current and improving charge collection at the interface of ETL/FTO. Moreover, dual am‐ZTO/SnO2 ETLs lead to large free energy difference (ΔG), improving electron injection from perovskite to ETLs. One additional electron pathway from perovskite to am‐ZTO is formed, which can also improve electron injection efficiency. A power conversion efficiency of 20.04% and a stabilized efficiency of 19.17% are achieved for the device based on dual am‐ZTO/SnO2 ETLs. Most importantly, the devices are fabricated at a low temperature of 150 °C, which offers a potential method for large‐scale production of PSCs, and paves the way for the development of flexible PSCs. It is believed that this work provides a strategy to design ETLs via controlling ΔG and interface contact to improve the performance of PSCs.

Tailoring the electronic properties of the SnO2 nanoparticle layer for n-i-p perovskite solar cells by Ti3C2TX MXene

Recently, it has been demonstrated that the use of SnO2 as the electron transport layer (ETL) of perovskite (PSK) solar cells (PSCs) yields high efficiency, which is comparable to that of the TiO2 layer with the same structure. At the same time, the SnO2-based PSCs show improved stability. Herein, the defects at the device interface are reduced and the efficiency of the planar PSCs is enhanced by improving the interface contact between the ETL and the perovskite (PSK) layer. As an essential amino acid, tyrosine (Tyr) is introduced into SnO2 to fill the oxygen vacancies in SnO2 films and improve the nucleation of PSK. From our analysis, it was found that the interface contact between the SnO2 ETL and the PSK layer was increased and the defects at the interface were reduced. In addition, it was demonstrated that the introduction of Tyr could effectively suppress the charge recombination and improve the electron extraction efficiency. As a result, a champion power conversion efficiency (PCE) of 22.17% was obtained from Tyr modified PSCs, owing to the enhanced PSK film quality and carrier extraction efficiency. On top of that, the Tyr-modified device still maintained 87% of the initial recorded PCE, which was stored in the ambient air (25 °C, 25% ± 5% RH) for 864 h without encapsulation.

Effect of lanthanum doped SnO2 on the performance of mixed-cation mixed-halide perovskite layer

In recent years, photovoltaic properties of hybrid perovskite solar cells (PSCs) have led to impressive improvement. Yet, there is still remain a challenge for large scale application and commercialization. Some of the reasons are the instability of the perovskite film and the lack of large‐scale and low‐cost manufacture techniques for electron transport layer (ETL). Tin oxide (SnO2) has emerged as a promising candidate for ETL, however, systematic exploration of its commercialized application in PSCs is still missing. Here, SnO2 ETL is prepared through an electron beam evaporation technology under low‐temperature process to realize large‐scale, low‐cost, and uniform manufacture. Hundreds of SnO2 ETL substrates can be fabricated at one time, which deserves industrial deployment. As a result, PSCs based on e‐beam evaporated SnO2 ETL and Cs‐containing blended perovskite absorber layer exhibit a power conversion efficiency (PCE) of up to 18.2% without any interface modification. Furthermore, the PSCs demonstrate remarkable long‐term stability, which remained at 97% of its initial PCE after being stored for over 34 days. The results demonstrate the great potential of the PSCs based on e‐beam evaporated SnO2 ETLs towards commercialization.

Synergetic effect of organic metal compound modified SnO2 in high performance perovskite solar cells

Improvement of nanopore structure SnO2 electron-transport layer for carbon-based CsPbIBr2 perovskite solar cells

In recent years, researchers have developed spray deposition technology to fabricate tin oxide electron transport layer (ETL) with the aim of manufacturing high‐efficiency, large‐area perovskite solar cell (PSC). However, the power conversion efficiency (PCE) of PSC based on sprayed SnO2 ETL remains inferior to that of the spin‐coated SnO2 ETL. Herein, the combined use of spray deposition and genetically engineered M13 bacteriophages for the deposition of M13‐SnO2 biohybrid ETL over large‐area (62.5 cm2) substrates is demonstrated. The spray‐deposited M13‐SnO2 ETLs exhibit mesoporous morphologies with >85% transmittance in UV–vis region. Through the use of M13‐SnO2 ETL, the sequential‐deposited PSCs achieve a maximum PCE of ≈22.1%. The improved performance of the PSC is attributable to the mesoporous morphology of M13‐SnO2 ETL that facilitates the growth of larger perovskite grains. The PSCs based on M13‐SnO2 ETLs also display highly consistent photovoltaic performance which manifests the excellent scalability of the spraying process. Furthermore, M13‐SnO2‐based PSCs exhibit higher ambient stability compared to the SnO2‐based PSCs, showing that the use of M13 bacteriophage is incredibly beneficial to both the efficiency and stability of PSCs.