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Efficient electron transport layer–free perovskite solar cells (ETL‐free PSCs) with cost‐effective and simplified design can greatly promote the large area flexible application of PSCs. However, the absence of ETL usually leads to the mismatched indium tin oxide (ITO)/perovskite interface energy levels, which limits charge transfer and collection, and results in severe energy loss and poor device performance. To address this, a polar nonconjugated small‐molecule modifier is introduced to lower the work function of ITO and optimize interface energy level alignment by virtue of an inherent dipole, as verified by photoemission spectroscopy and Kelvin probe force microscopy measurements. The resultant barrier‐free ITO/perovskite contact favors efficient charge transfer and suppresses nonradiative recombination, endowing the device with enhanced open circuit voltage, short circuit current density, and fill factor, simultaneously. Accordingly, power conversion efficiency increases greatly from 12.81% to a record breaking 20.55%, comparable to state‐of‐the‐art PSCs with a sophisticated ETL. Also, the stability is enhanced with decreased hysteresis effect due to interface defect passivation and inhibited interface charge accumulation. This work facilitates the further development of highly efficient, flexible, and recyclable ETL‐free PSCs with simplified design and low cost by interface electronic structure engineering through facile electrode modification. [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]

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]

[Display omitted] • A facile surface modification method using alkylamines to treat the CsPbI 3 surface is proposed. • HDA treatment can ameliorate defect passivation and energy level alignment to reduce voltage loss. • A champion PCE of 18.21% is achieved for the HDA-treated inverted CsPbI 3 PSCs. • HDA treatment promotes the humidity stability both of CsPbI 3 films and solar cells. Inorganic CsPbI 3 perovskite has been regarded as a kind of promising light-harvesting material due to its outstanding photoelectrical characteristics especially in perovskite solar cells (PSCs). However, there are still some problems hindering its further development, among which non-radiative recombination induced by traps and voltage loss are very pivotal. Here, the passivation of surface defects and energy level alignment of perovskite films are greatly ameliorated by facile surface modification with alkylamines. It is found that the undercoordinated Pb2+ are effectively passivated by the terminal amino group, leading to significantly reduced surface trap density, while the charge lifetime of treated perovskite films is prolonged. Besides, the bilateral amino groups from hexanediamine (HDA) can provide additional hydrogen bond to coherently connect the PbI 6 4− octahedra. Moreover, gradient energy levels are created after surface treatment, which promote the carriers transfer and reduce the voltage deficit. Consequently, a champion power conversion efficiency (PCE) of inverted CsPbI 3 PSCs over 18 % with higher fill factor (FF) of 81.21 % and open circuit voltage (V OC) of 1.10 V is obtained compared to the pristine device with a lower PCE of 12.69 % (V OC of 1.01 V, and FF of 62.49 %). Besides, the unencapsulated device with HDA treatment exhibits good stability with keeping 80 % of its initial efficiency after being aged for 1000 h at 35 % relative humidity. Our work can offer a facile but effective approach for the development of highly efficient and stable inverted CsPbI 3 PSCs. [ABSTRACT FROM AUTHOR]