Inverted planar heterojunction (PHJ) perovskite solar cells have attracted great attention due to their advantages of low-temperature fabrication on flexible substrates by solution processing with high efficiency. Poly(3,4ethylenedioxythiophene): polystyrenesulfonate (PEDOT:PSS) is the most widely used hole transport layer (HTL)in inverted PHJ perovskite solar cells; however, the acidic and hygroscopic nature of PEDOT: PSS can cause degradation and reduce the device stability. In this work, we demonstrated that low-cost solution-processed hydrophobic copper iodide (CuI) can serve as a HTL to replace PEDOT: PSS in inverted PHJ perovskite solar cells with high performance and enhanced device stability. Power conversion efficiency (PCE) of 13.58% was achieved by employing CuI as a HTL, slightly exceeding PEDOT: PSS based device with PCE of 13.28% under the same experimental conditions. Furthermore, the CuI based devices exhibited better air stability than that of PEDOT: PSS based devices. The results indicate that low-cost solution-processed CuI is a promising alternative to PEDOT: PSS HTL and could be widely used in inverted PHJ perovskite solar cells.

Stability issues and high material cost constitute the biggest obstacles of a perovskite solar cell (PVSC), hampering its sustainable development. Herein, we demonstrate that, after suitable surface modification, the low-cost cerium oxide (CeO ) nanocrystals can be well dispersed in both polar and nonpolar solvents and easily processed into high-quality electron transport layers (ETLs). The inverted PVSC with the configuration of "NiMgLiO/MAPbI/[6,6]-phenyl-C-butyric acid methyl ester (PCBM)/CeO " has achieved a high efficiency up to 18.7%. Especially, the corresponding devices without encapsulation can almost keep their initial PCEs in 30% humidity-controlled air in the dark for 30 days and also show no sign of degradation after continuous light soaking and maximum power point tracking for 200 h in a N atmosphere. These results have been proved to be associated with the dual functions achieved by the PCBM/CeO bilayer ETLs in both efficient electron extraction and good chemical shielding. Furthermore, an all inorganic interfacial layer based PVSC with the configuration of "NiMgLiO/MAPbI/CeO " has also achieved a promising efficiency of 16.7%, reflecting the potential to fabricate efficient PVSCs with extremely low cost.

Perovskite solar cells are promising candidates for next-generation photovoltaics.Fullerenes and their derivatives can act as efficient electron transport layers, interfacial modification layers and/or trap state passivators in perovskite solar cells, which play an important role in increasing efficiency, reducing current hysteresis, and enhancing device stability. Herein, recent progresses of fullerenes and their derivatives used in perovskite solar cells are reviewed, with a particular emphasis on fullerene chemical structures that affect performance of the devices. Potential candidates of fullerenes that could further improve device performance and stability are also discussed.

Low-temperature, solution-processed cerium oxide can serve as a promising electron transport layer to replace commonly used TiO2 in planar perovskite solar cells, with high efficiency and enhanced stability.

Perovskite solar cells (PSCs) with TiO2 materials have attracted much attention due to their high photovoltaic performance. Aligned TiO2 nanorods have long been used for potential application in highly efficient perovskite solar cells, but the previously reported efficiencies of perovskite solar cells based on TiO2 nanorod arrays were underrated. Here we show a solvothermal method based on a modified ketone-HCl system with the addition of organic acids suitable for modulation of the TiO2 nanorod array films to fabricate highly efficient perovskite solar cells. Photovoltaic measurements indicated that efficient nanorod-structured perovskite solar cells can be achieved with the length of the nanorods as long as approximately 200 nm. A record efficiency of 18.22% under the reverse scan direction has been optimized by avoiding direct contact between the TiO2 nanorods and the hole transport materials, eliminating the organic residues on the nanorod surfaces using UV-ozone treatment and tuning the nanorod array morphologies through addition of different organic acids in the solvothermal process.

A low‐temperature solution‐processed strategy is critical for cost‐effective manufacture of flexible perovskite solar cells (PSCs). Based on an aqueous‐processed TiO2 layer, and conventional fullerene derivatives replaced by a pristine fullerene interlayer of C60, herein a facile interface engineering for making all‐solution‐processed TiO2/C60 layers in flexible n‐i‐p PSCs is reported. Due to the improvement of the perovskite grain quality, promotion of interfacial charge transfer and suppression of interfacial charge recombination, the stabilized power conversion efficiency for the flexible PSCs reaches as high as 16% with high bending resistance retention (≈80% after 1500 cycles) and high light‐soaking retention (≈100% after 100 min). In addition, the stabilized efficiency is over 19% for the rigid TiO2/C60‐based PSCs. The present work with the facile low‐temperature solution process renders the practicability for high‐performance flexible PSCs applied to wearable devices, portable equipment, and electric vehicles.

Tuning the polarity of green antisolvents (using various ethers) allows high control over the purity of the intermediate phase of triple-cation lead halide perovskite thin films.

In regular perovskite solar cells (PSCs), the commonly used electron transport layer (ETL) is titanium oxide (TiO2). Nevertheless, the preparation of a high-quality TiO2 ETL demands an elevated-temperature sintering procedure, unfavorable for fabrication of PSCs on flexible substrates. Besides, TiO2-based devices often suffer from notorious photocurrent hysteresis and serious light soaking instability, limiting their potential commercialization. Herein, a novel pyridine-functionalized fullerene derivative [6,6]-(4-pyridinyl)-C61-ethyl acid ethyl ester (PyCEE) was synthesized and applied as an ETL to replace TiO2 in n–i–p PSCs. PyCEE-based devices achieved a champion power conversion efficiency (PCE) of 18.27% with significantly suppressed hysteresis, superior to that of TiO2-based devices. PyCEE has suitable energy levels and high electron mobility, which facilitate electron extraction/transport. Besides, the pyridine moiety within PyCEE affords coordination interactions with the Pb2+ ion within CH3NH3PbI3, passivating the trap states of CH3NH3PbI3 and thus improving the device performance and suppressing hysteresis greatly. Moreover, PyCEE ETLs were applied in flexible PSCs, achieving a PCE of 15.25%. Our results demonstrated the applicability of PyCEE ETLs in flexible devices and provided new opportunity for the commercialization of PSCs.