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Perovskite solar cells (PSCs) have shown an impressive power conversion efficiency of 26.1%, while their upcoming commercialization urgently needs to solve the stability problem. Among numerous stability issues of PSCs, little attention is paid to reverse bias stability. When some cells of the module are shaded by irresistible factors, this will cause the current of the illuminated part to flow through the shaded cells as a reverse current and force them to be under reverse bias. Herein, the breakdown mechanism dominated by different reverse bias regions of a prototype electron transport layer free PSCs is distinguished. And, it is confirmed that PSCs present a thought‐provoking dynamic reverse bias (DRB) behavior and variable reverse breakdown voltage (VRB), which is essentially distinct from classic solar cells. Specifically, VRB is significantly affected by voltage scan rate, range and direction, and illumination. The underlying mechanism is explained by drift‐diffusion modeling taking into account the electric field generated by directional ion migration. The latter can hinder the movement of charge carriers and cause the observed variable VRB and DRB behavior. Predictably, the understanding of the dynamic process is crucial to establish a standard VRB measurement procedure and further promote the commercialization of PSCs. [ABSTRACT FROM AUTHOR]

Efficient electron transport layer-free perovskite solar cells (ETL-free PSCs) are promising designs because they offer low-cost, simpler device configuration and greatly promote the large area flexible application of PSCs. Meanwhile, compared to traditional PSCs with ETL, the development of ETL-free PSCs is hindered by their low performance due to serious interfacial energy loss. Herein, we reveal that ETL-free devices with relatively low carrier lifetimes of perovskite films exhibit more substantial photogenerated carrier loss, resulting in a lower electron-injection rate at the FTO (fluorine-containing tin oxide)/perovskite interface, which is mainly responsible for the performance loss. Moreover, we demonstrate that improving the carrier lifetimes of perovskite films can remedy the poor carrier extraction efficiency at the FTO/perovskite interface through three typical perovskite films. Similarly, for all-inorganic perovskite with lower carrier lifetime and hole transport layer-free devices, prolonging carrier lifetime may be an important measure to improve the device performance. Benefiting from this discovery, increasing the carrier lifetime of the perovskite films can counterbalance the inferior device interfaces, endowing the ETL-free PSCs with high performance close to that of the ETL devices. Our research provides insights into ETL-free PSCs and offers opportunities for high-performance ETL-free PSC device design. [ABSTRACT FROM AUTHOR]

CsPbI2Br all-inorganic perovskite solar cells (PSCs) have attracted much attention due to their suitable bandgap and outstanding thermostability. However, the large energy loss of CsPbI2Br PSCs generally endows low open circuit voltage (VOC) and unsatisfactory power conversion efficiency (PCE), which severely hamper its further development. Herein, we proposed a facile route to modify the ZnO electron transporting layer (ETL) by in situ chemical doping strategy with metal ions. The doped ZnO ETL with Pb(Ac)2 or CsAc cannot only effectively tune its energy levels, conductivity, and charge extraction but also ameliorate the crystallization and morphology of upper perovskite films. Particularly, Pb(Ac)2-doped ZnO (ZnO:Pb) induces an energy level offset of 0.15 eV relative to the conduction band of CsPbI2Br with largely reduced Ohmic loss. Thus, the highest VOC is significantly boosted to above 1.3 V for the CsPbI2Br PSCs with a champion PCE of 16.36%, while the reference PSC just yields a moderate PCE of 14.43% with a low VOC of 1.168 V. Moreover, considerable improvements in device stability are achieved for the PSCs with doped ZnO ETLs than those of the ZnO-based device. Our work provides a promising strategy to alleviate the VOC deficit toward the attainment of highly efficient and stable PSCs. [ABSTRACT FROM AUTHOR]

In inverted perovskite solar cells, the [6,6]-phenyl-C61-butyric acid methyl ester (PCBM)/Ag back interface is quite important because serious recombination occurs and H2O/O2 directly attacks this interface to induce device instability. Here, bi-functional dipole layers are applied at the interface aiming at improving the charge transport and device stability simultaneously. Silane with -CF3 end group anchored on the PCBM surface induces more effective dipole effect than that with (CH2)7-CH3 end functional silane, bending the interface energy level to promote electron transport and reduce recombination. The hydrophobic nature of -CF3 also enhances the durability of the device. This work highlights the back surface dipole management method to achieve efficient and stable perovskite solar cells. [ABSTRACT FROM AUTHOR]

Electron transport layer (ETL)‐free perovskite solar cells (PSCs) have witnessed great progress via material and interface engineering. Enlighten by the wisdom from an old story of efficient silicon solar cells design, highly efficient MINP (metal/insulator/n‐type perovskite/p‐type spiro‐MeOTAD) PSC with polar insulating inter‐layer (PIIL) modified fluorine‐doped tin oxide (FTO) is reported as electron selective contact. The PIIL forms metal‐insulator‐semiconductor (MIS) junction with FTO and perovskite layer, while the n‐type perovskite forms P‐N junction with p‐type spiro‐MeOTAD. Unlike the classic MINP silicon solar cells where the I‐layer is usually neutral tunneling layer, the PIIL here optimizes the energy level alignment at the FTO/perovskite interface with its intrinsic electronic polarity while acting as an effective tunneling layer. Also, the functional group of the PIIL passivates the FTO/perovskite interface defects thus suppressing carrier recombination thereof and enhancing all device performance parameters simultaneously. Accordingly, the power conversion efficiency is greatly improved from 12.82% to 19.75%. With the enhanced electron collection and decreased carrier recombination of the MIS junction, this collaborative effect of interface engineering and defect passivation contribute to more stable ETL‐free PSC with less hysteresis. This work highlights the potential of novel device and interface design for simple‐structured, efficient and cost‐effective PSCs. [ABSTRACT FROM AUTHOR]

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]

A facile and low‐temperature solution processed UV/ozone process has been proposed for fabricating TiO2 layer, making it possible to fabricate planar perovskite solar cells at low temperature. UV/ozone photo‐annealing treatment could easily eliminate the organic components, resulting in high quality amorphous TiO2 films with high transparency, electrical conductivity, and hydrophilicity. In addition, perovskite solar cells with the UV/ozone‐treated TiO2 electron transport layer exhibiting the best power conversion efficiency of 11.58% for rigid substrate and 7.33% for flexible substrate, respectively. The results clearly indicate that UV/ozone photo‐annealing treatment is a simple and effective process of fabricating high performance flexible perovskite solar cells. Fully low‐temperature solution‐processed perovskite solar cells (PSCs) are fabricated using UV/ozone (UV/O3) treated TiO2 film as an electron transport layer. UV/O3 treatment increases the electrical conductivity and wettability of the TiO2 film, and therefore improves the performance of PSCs. By optimizing the processing time of UV/O3 treatment, the power conversion efficiency of the best rigid and flexible device is 11.58% and 7.33%, respectively. [ABSTRACT FROM AUTHOR]