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Rough dense sol-gel-derived titanium dioxide (TiO 2 ) electron-transport layers (ETLs) and smooth organolead halide perovskite (PVK) films for pseudo-planar heterojunction perovskite solar cells (P-PH PVKSCs) were fabricated by a facile one-step dip-coating method. The highly compact TiO 2 ETLs and uniform PVK films endow the device a high power conversion efficiency (PCE) of over 11%, which was nearly identical to that of a reference device (12%) fabricated by conventional spin-coating. Furthermore, the device showed no pronounced hysteresis when tested by scanning the voltage in a forward and backward direction, showing the potential of facile and waste-free dip-coating in replacing of spin-coating for large area perovskite solar cells preparation. Lastly, the hysteresis was compared and discussed and models regarding the abnormal hysteresis, roll-over and current peak phenomena were proposed as well. [ABSTRACT FROM AUTHOR]

Device modeling of CH 3 NH 3 PbI 3−x Cl x based electron transport layer-free planar perovskite solar cells was performed. The simulation was conducted by the program SCAPS (Solar Cell Capacitance Simulator). With appropriate physical parameters, a high open-circuit voltage of 1.04 V close to results reported experimentally was successfully reproduced in the simulation. Simulation results revealed a great dependence of PCE on the thickness and defect density of the perovskite layer. An optimum perovskite thickness of about 500 nm was confirmed and it well consistent with the thickness range of real devices was derived. Meanwhile, parameters including the FTO/perovskite interface defect density as well as the doping concentration of the front contact (FTO) were identified to significantly influence the performance of the device. In particular, the interface quality at the FTO/perovskite interface has greater impact on the device parameters than that at the perovskite/HTL interface, which suggests that more attention should be paid to the front FTO/perovskite interface to further enhance the performance of electron transport layer-free device. Appropriate interface defect passivation to reduce the interface defect density to the order of ~10 15 cm −3 is necessary and urgently needed. Lastly, the effect of the electron and hole mobility and carrier diffusion length of CH 3 NH 3 PbI 3−x Cl x were also analyzed and the results revealed that the mobility and diffusion length experimentally reported (~1.0 µm) are large and long enough for high efficiency. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PVKSCs) are an attractive technology that finds their potential in the field of renewable energy sources. Transparent conductive oxides including fluorine-doped tin dioxide (FTO) and indium tin oxide (ITO) with high optical transmittance and low electrical resistivity are key components in PVKSCs. While commercial FTO or ITO either requires high temperature and high vacuum process or contains rare indium element, which will increase the production cost of PVKSCs. Here we report efficient electron-transport layer (ETL) free planar PVKSCs using the recycled FTO/glass substrates from degraded devices. By simple and low-temperature processes including organic solvent washing, ultrasonic cleaning and UV ozone treatment, the discarded substrates can be readily reused for fabricating ETL-free planar PVKSCs. The UV–vis optical transmission, crystal structure, sheet resistance, surface morphology, elemental composition and static contact angles measurement of the original and recycled FTO/glass substrates (one time and two times) were measured and compared. Planar ETL-free devices with power conversion efficiencies of about 10% have been achieved by adopting the recycled FTO/glass substrates, which are comparable to that of the devices based on the original FTO substrates, suggesting the feasibility of recycling the FTO/glass substrates from degraded devices for fabricating ETL-free PVKSCs. [ABSTRACT FROM AUTHOR]

Planar perovskite solar cells with a p–i–n structure use both hole-transport layers and electron-transport layers to promote collection of photogenerated holes and electrons for achieving high performance, wherein a high temperature processed compact and mesoporous titanium dioxide are usually required. We report here efficient perovskite solar cells grown directly on ultraviolet–ozone treated fluorine-doped tin oxide (FTO) substrates without using any electron-transport layers. The morphology, structure, optical–electrical properties of perovskite films deposited on FTO substrates with and without ultraviolet–ozone treatment and their corresponding devices׳ performance have been studied and compared. Ultraviolet–ozone treatment of FTO substrates improves the smoothness and coverage of CH 3 NH 3 PbI 3− x Cl x films, which avoids direct contact between FTO and hole-transport layer. A planar electron-transport layer free device with a power conversion efficiency of over 10% has been achieved, suggesting that the widely adopted electron-transport layer is not a requirement for an efficient device. [ABSTRACT FROM AUTHOR]

We report planar heterojunction perovskite solar cells with tetrafluoro-tetracyanoquinodimet-hane (F4-TCNQ) doped spiro-MeOTAD by solvent treatment as hole transport layer. The non-hygroscopic F4-TCNQ doped spiro-MeOTAD plays the same role as Li-bis (trifluoromethanesulfonyl) imide doped spiro-MeOTAD in perovskite solar cells, endowing the device both high efficiency and good stability. The F4-TCNQ dopant was optimized to enhance the conductivity and adjust the highest occupied molecular orbital of spiro-OMeTAD to match the valence band maximum of perovskite for efficient hole extraction, which results in a high fill factor, open circuit voltage and short current density, simultaneously. Device including the F4-TCNQ doped spiro-MeOTAD exhibits a power conversion efficiency of 10.59%, which is a 160% improvement relative to that of the control device with the pristine spiro-MeOTAD as hole transport layer. Time-dependent solar cell performance measurements revealed significantly improved air stability for perovskite solar cells with the F4-TCNQ doped spiro-MeOTAD hole transport layer. [ABSTRACT FROM AUTHOR]

The morphology, structure, optical and electrical properties of perovskite films treated by two different annealing methods with different annealing temperature ramp and their corresponding device performance have been studied and compared. Annealing temperature ramp significantly influences the surface morphology and optical properties of perovskite films which determines the performance of solar cells which determines the performance of solar cells . The perovskite films treated by one-step direct annealing method tend to exhibit irregular and weak ultraviolet–visible absorption spectrum, which can easily result in great variation in the final performance of solar cells. While multi-step slow annealing is beneficial for preparing highly uniform and well-crystallized perovskite films, and thus these devices present tightly-distributed performance parameters. The best device treated by multi-step slow annealing method showed a short circuit current density of 21.49 mA/cm 2 , an open circuit voltage of 0.988 V, a fill factor of 64.86%, and a power conversion efficiency (PCE) of 13.58%, which is a 57% enhancement of the overall PCE relative to 8.65% of the device treated by one-step annealing method. These findings suggest that optimized slow temperature ramp is necessary to prepare high-efficient and well-reproducible perovskite solar cells. [ABSTRACT FROM AUTHOR]

In Sn-Pb based low bandgap perovskite solar cells (LB-PSCs), the large energy loss of ~0.5 eV lags its development, originating from unfavorable band alignment at the interface and serious charge recombination in the device. Here, judiciously designed graphene quantum dots by functional N/Cl doping are applied at PEDOT:PSS/perovskite interface to modulate the energy level and charge transfer simultaneously. Among three designed graphene quantum dots, the N, Cl codoped one (N,Cl-GQDs) induces the best band alignment, because of the enhanced p-doping. Besides, N,Cl-GQDs best regulate the charge distribution and passivate the defect states at the interface by π-conjugated effect and electronegative Cl, paving the way for efficient interface charge transport. Upon N,Cl-GQDs optimization, the FA 0.6 MA 0.4 Sn 0.6 Pb 0.4 I 3 based PSCs achieves impressive efficiency of 21.5% (1 sun, AM1.5) with a high photovoltage of ~0.89 V (energy loss of ~0.36 eV) and fill factor over 80%, which are among the best parameters in reported LB-PSCs. The N,Cl-GQDs modified device exhibits the best shelf stability after 1000 h, due to the least trap states and reformative interface. This work highlights designed graphene quantum dots for photovoltaic applications. [Display omitted] • Designed GQDs are applied at PEDOT:PSS/PVK interface to modulate the energy level and charge transfer simultaneously. • N,Cl-GQDs regulate the interface charge distribution and passivate the defects, guaranteeing efficient charge transport. • Sn-Pb based PSCs achieve impressive efficiency of 21.5%, which are among the best parameters in reported low bandgap-PSCs. [ABSTRACT FROM AUTHOR]

The self-organization of the polymer in solar cells based on regioregular poly(3-hexylthiophene)(RR-P3HT):[6, 6]-phenyl C61-butyric acid methyl ester is studied systematically as a function of the room temperature (RT) (varied from 300 K to 290 K). Optimal self-organized structures within the RR-P3HT:PCBM films are achieved by varying spin speed and time as well as the temperature at which the spin casting process occurs. These blend films are characterized by UV–vis absorption spectroscopy, atomic force microscopy, and X-ray diffraction measurements. The optimum device efficiency can be achieved in naturally dried devices when spin coating within the temperature range 292–294 K. Both the power conversion efficiency (PCE) and fill factor (FF) of the optimum devices show a plateau region, with PCEs exceed 4% and FFs close to 0.70. For RT < 290 K, the corresponding devices show a wide distribution of performance parameters for the unhomogeneous active layer. While for RT > 296 K, the short current density, FF and PCE of the corresponding devices are gradually decreased, suggesting that there is a major change in the ordered structure of the polymer. Based on the results, it is demonstrated that high performance device can be achieved just by natural drying the active layer at RT condition in air condition without further thermal treatments. [ABSTRACT FROM AUTHOR]

An effective and facile surface optimization method is conducted by spin-coating the solution containing Al(NO 3 ) 3 upon compact TiO 2 (c-TiO 2 ) electrode for enlarging the performance of planar perovskite solar cells (p-PSCs). Meanwhile, the influence of Al(NO 3 ) 3 solution concentration on efficiency performance of p-PSCs is also carefully investigated. The study results highlight that a discrete Al 2 O 3 film can be formed on c-TiO 2 electrode to passivate superficial oxygen vacancies defects and create a pleasurable surface topography, alone with high optical transparency. As a consequence, the champion device based on the modified c-TiO 2 (Al-TiO 2 ) via spinning 0.7 wt% Al(NO 3 ) 3 solution drastically yields an enhanced power conversion efficiency of 14.75% as well as enjoys superior device stability compared to its counterpart based on bare c-TiO 2 . Through a further analysis, the fact that Al-TiO 2 can effectively augment the charge collection and abate charge recombination efficiency by the suppression of oxygen vacancy defects at Al-TiO 2 /CH 3 NH 3 PbI 3-x Cl x interface than that of bare c-TiO 2 without modification is unveiled. Those findings provide an insight into the correlation between p-PSCs performance and the microscopic characteristics of c-TiO 2 , and put forward an effective measure to further promote the performance of p-PSCs for their record efficiency. [ABSTRACT FROM AUTHOR]

Long-chain insulating polymers dissolved in perovskite precursor solution can assemble the polymer scaffold acted as the function of TiO 2 porous layer to improve the quality of the perovskite films. Here, perovskite films with high electronic quality were prepared by mediating nucleation and crystal growth. Polymer post treatment can induce Lewis acid-base reaction with PbCl 2 , which alleviates the reaction velocity between PbCl 2 and CH 3 NH 3 I, and then retard perovskite crystallization. The interactions between the perovskite films and polymer with different concentration are addressed to interpret the function and evolution of the polymer long-chains during the annealing process. These solar cells exhibit efficiency more than 15% with small variation. Our work demonstrates the value of retarding nucleation and crystal growth by Lewis acid-base adducts for high-quality perovskite films. [ABSTRACT FROM AUTHOR]

The power conversion efficiency (PCE) of ternary organic solar cells (OSCs) based on PTB7-Th:PCDTBT:PC 70 BM with good air stability needs to be further improved. We report here 2 min methanol solvent treatment of the active layer of ternary OSCs based on PTB7-Th:PCDTBT:PC 70 BM can significantly boost efficiency up to 9.60%, which exhibits a 30.4% improvement compared to that of 7.36% for the device without methanol solvent treatment. The performance improvement is mainly due to the enhanced light absorption, efficient charge transfer and optimized bulk morphology in the ternary active layer. Meanwhile, the air stability of the methanol solvent treated device can be clearly improved by the removal of residual DIO in the active layer. The PCE of the 2 min methanol treated device could retain 95.4% of the initial value after 7 days of storage in air. Our results indicate that methanol solvent treatment is a simple but effective strategy to boost efficiency and air stability of ternary OSCs based on PTB7-Th:PCDTBT:PC 70 BM. [ABSTRACT FROM AUTHOR]

A ZnO-Ge bilayer was proposed as an electron transport layer (ETL) in inverted ternary organic solar cells (OSCs). The energy level alignment, surface morphology, optical and electrical properties, and interface charge transfer were investigated to understand the impact of the additional Ge NPs layer. The results indicated that apart from improving the energy level alignment, the Ge NPs layer optimizes the interfacial contact between the active layer and ETL. Moreover, the ZnO-Ge bilayer shows better optical transmittance and perpendicular electrical transport properties compared to that of ZnO NPs layer. Benefit from the enhanced charge transfer from the active layer to ETL, the champion power conversion efficiency (PCE) was significantly increased to 9.15% by introducing the additional Ge layer, which exhibited a 18.4% improvement compared to that of the ZnO-only devices. Our results demonstrated the feasibility of ZnO-Ge bilayer as the ETL for high-performance OSCs. [ABSTRACT FROM AUTHOR]

Ternary bulk heterojunctions (BHJs) are promising candidates that can improve the power conversion efficiencies (PCEs) of organic solar cells (OSCs). In this paper, a ternary OSC with two donors, including one wide bandgap polymer poly[ N -9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT), one low bandgap polymer Poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2- b :4,5- b ′]dithiophene-co-3-fluorothieno[3,4- b ]thiophene-2-carboxylate] (PTB7-Th), and one acceptor [6,6]-phenyl C70 butyric acid methyl ester (PC 70 BM), is fabricated in atmospheric conditions. By incorporating a 20% content of PCDTBT, an optimized PCE of 7.86% for ternary OSC is characterized by a short-circuit current density ( J sc ) of 15.21 mA cm −2 , a fill factor of 69.70% and an open-circuit voltage ( V oc ) of 0.74 V. The V oc values increased steadily from 0.73 to 0.86 V as the increase of PCDTBT fraction, which indicates that the V oc of ternary OSC is not limited by the smallest one of the corresponding binary OSC. We show that the J sc of the ternary OSC is better than those of the binary OSC in virtue of the complementary polymer absorption and cascade energy levels, as well as optimized morphology of the ternary system. Furthermore, the lifetime of the devices with PCDTBT is greatly enhanced. This work indicates that two donors (PTB7-Th/PCDTBT) ternary BHJs system provide a simple and effective method to improve the performance and also the stability of OSCs. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) have attracted great attentions due to their excellent photovoltaic performance. Further improvement of device efficiency is limited by the recombination of the charge carriers even a heterojunction-based architecture is employed. Herein, we discovered that a simple surface modification of the perovskite film by incorporating isopropyl alcohol (IPA) post-treatment could convert the top surface to be more n-type, which spontaneously formed an n/n+ homojunction between the bulk (weak n type (n)) and the surface (more n-type (n+)) in a single perovskite film. A reconstruction toward a PbI 2 -rich top surface was induced by the remove of excess formamidinium iodide dissolved in a polar solvent IPA. This reconstructed n/n+ homojunction lead to the enlarged built-in electric field for efficient charge separation and transport of the photogenerated carriers. The inverted PSCs with the reconstructed n/n+ homojunction contribute to improve efficiency and narrow their efficiency gap with conventional n-i-p type devices. Our result suggests that the homojunction structure is an effective approach to reduce carrier recombination loss and achieve highly efficient PSCs. [Display omitted] • A facile surface homojunction reconstruction is achieved by solvent treatment. • A PbI 2 -rich perovskite surface is induced by the remove of excess FAI. • The reconstructed n/n+ homojunction brings about the enlarged built-in electric field. • The reconstructed n/n+ homojunction contributes to improved photovoltaic efficiency. [ABSTRACT FROM AUTHOR]

A rapid annealing technique for fabricating perovskite materials via microwave radiation in air condition is presented. A planar-heterojunction perovskite device via microwave radiation within 6 min exhibits an efficiency of 10.29%, compared to 11.08% for a 90 min heating-annealed device in inert atmosphere, which is higher than that (8.04%) of a heating-annealed device in air condition under high humidity (∼60%). We believe that the microwave annealing technique provides a fast and less energy-intensive process for fabricating ideal perovskite active layers for high performance solar cells. [ABSTRACT FROM AUTHOR]

Ultrathin and compact SnO x amorphous layers derived from SnCl 4 were introduced at the interface of electron transport layer (ETL)/perovskite or FTO/ETL to enhance the electron coupling between layers, passivate the trapping defects and optimize the energy level alignment. As results of the increased interface electron collection and reduced interface recombination, the planer perovskite solar cell (PSC) with SnO 2 nanocrystal (NC) ETL pre-treated by SnCl 4 (Cl-SnO 2) shows the power conversion efficiency (PCE) enhancement from 16.3% to 18.6%, and the device hysteresis has also been significantly restrained. In comparison, the planer PSCs with traditional SnCl 4 (SnO 2 -Cl) post-treated SnO 2 NC ETL makes the PCE increased from 16.3% to 17.3%. These results indicate that both two kinds of treated ways could improve the performance of the PSCs but compared with the post-treatment process, the devices based on Cl-SnO 2 pre-treated ETL present superior performance, which is attributed to the closer contact and enhanced electron coupling between FTO and SnO 2 NC ETL with Cl-SnO 2 in between. An ultrathin compact SnO 2 layer derived from SnCl 4 was introduced at the interface of FTO/SnO 2 to enhance the electron coupling and passivate the trapping defects between layers. And the performance is significantly improved compared with devices with untreated or traditional post-treated SnO 2 nanocrystal electron transport layers. Image 1 • Ultrathin and compact SnO x layer is introduced at the interface of FTO/Electron transport layer (ETL). • The devices with SnO 2 ETL pre-treated by SnCl 4 shows the power conversion efficiency enhancement from 16.3% to 18.6%, and the device hysteresis has also been significantly restrained. • This paper also fabricated devices with SnCl 4 post-treated SnO 2 ETL for comparing to further show the advantages of the new treatment way. [ABSTRACT FROM AUTHOR]