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The elimination of methylammonium (MA) cation from mixed tin–lead (Sn–Pb) narrow‐bandgap (NBG) perovskites is an effective approach to enhance the operational stability of all‐perovskite tandem solar cells (TSCs). Unfortunately, the uncontrolled nucleation and crystallization processes of MA‐free Sn–Pb perovskites usually lead to inferior film quality and device performance. Herein, a bimolecular crystallization modulation strategy is reported by using guanidine thiocyanate (GuaSCN) and aminoacetamide hydrochloride (AHC) together as additives to improve the film quality of MA‐free Sn–Pb perovskites. It is demonstrated that the use of bimolecular additives can effectively improve the crystallinity, increase the grain size, and induce a preferred (100) orientation for the corresponding films, leading to high‐quality absorber with considerably reduced defect density and suppressed non‐radiative recombination. In addition, the bimolecular additives can reduce the self‐p‐doping hole concentration within the perovskite films and enhance the charge extraction at the perovskite/electron transport layer interface. The modified NBG perovskite solar cells deliver a power conversion efficiency (PCE) of 22.14%. Coupled with the wide‐bandgap (WBG) subcell, the all‐perovskite TSCs give a champion certified PCE of 27.15%, which is the highest certified PCE for MA‐free all‐perovskite TSCs. Encapsulated tandem devices maintain 90% of the initial PCE after 473 h operation. [ABSTRACT FROM AUTHOR]

Inorganic perovskite solar cells (I‐PSCs) have attracted great attention due to the high thermal stability of inorganic perovskites versus the organic–inorganic perovskites. To ensure the thermal stability of I‐PSCs, using effective and stable inorganic charge‐transporting layers (CTLs) to replace organic ones is quite desirable. The use of low‐temperature‐prepared inorganic CTLs can also lower the total cost of I‐PSCs. Herein, a general strategy to prepare high‐quality inorganic nanoparticles‐based electron transport layers (ETLs) below 70 °C by ligand exchange on top of inorganic perovskites is developed. The ETLs possess a suitable energy‐level structure, favorable conductivity, and chemical stability. Furthermore, all‐inorganic CTLs‐based CsPbI2Br I‐PSCs with p–i–n architecture are fabricated without using any thermally unstable organic components. Consequently, the as‐fabricated I‐PSCs based on CdS ETLs yielded the highest power conversion efficiency (PCE) of up to 15.04%, among the most efficient CsPbI2Br inverted PSCs. Inspiringly, the unencapsulated all‐layer‐inorganic PSCs present outstanding stabilities, which maintained 94.8% and 95.2% of their initial PCEs after aging at 85 °C in the dark and operating under continuous light illumination at 45 °C for 480 h in N2 atmosphere, respectively. [ABSTRACT FROM AUTHOR]

Perovskite solar cells have emerged as the next‐generation high‐efficiency solar cell, but their absorption is mostly limited to the visible (vis) range. One possible solution is to integrate near‐infrared (NIR)‐to‐vis photon upconversion (UC). Herein, we show the first example of endowing perovskite solar cells with NIR sensitivity by using solid films showing NIR‐to‐vis UC based on triplet‐triplet annihilation (TTA). A high TTA‐UC efficiency of 4.1±0.3 % at an excitation intensity of 125 W/cm2 is achieved by sensitizing a rubrene (acceptor) triplet with an osmium (Os) complex donor having singlet‐to‐triplet (S−T) absorption in the NIR range, and by increasing the fluorescence quantum yield through energy harvesting to a highly fluorescent collector. In particular, our spectroscopic studies indicate that the upconverted acceptor singlet energy is almost selectively transferred to the collector rather than being quenched by the donor. By attaching the TTA‐UC film behind a semi‐transparent perovskite solar cell, a photocurrent generation is observed under excitation at 938 nm. [ABSTRACT FROM AUTHOR]

In the past decade, the efficiency of perovskite solar cells quickly increased from 3.8% to 25.2%. The quality of perovskite films plays vital role in device performance. The films fabricated by solution‐process are usually polycrystalline, with significantly higher defect density than that of single crystal. One kind of defect in the films is uncoordinated Pb2+, which is usually generated during thermal annealing process due to the volatile organic component. Another detrimental kind of defect is Pb0, which is often observed during the film fabrication process or solar cell operation. Because the open circuit voltage has a close relation with the defect density, it is thus desirable to passivate these two kinds of defects. Here, a molecule with multiple ligands is introduced, which not only passivates the uncoordinated Pb2+ defects, but also suppresses the formation of Pb0 defects. Meanwhile, such a treatment improves the energy level alignment between the valence band of perovskite and the highest occupied molecular orbital of spiro‐OMeTAD. As a result, the performance of perovskite solar cells significantly increases from 19.0% to 21.4%. [ABSTRACT FROM AUTHOR]

Defective perovskite surfaces severely limit the development of inverted perovskite solar cells (PSCs). Here, the impacts of surface treatment are systematically investigated with organic ammonium salts, namely piperidinium iodide (PpI) and piperazinedihydroiodide (PDI), on the performance of the formamidinium‐cesium (FACs)‐based PSCs. These results indicate that PpI, with its high dipole moment, tends to form 1D structures on the perovskite surface, which hinders electron transport. By contrast, PDI post‐treatment does not lead to the formation of such structures; instead, it forms a thin passivation layer that homogenizes the electric potential across the perovskite surface. This merit results in a favorable alignment of energy levels and a significant reduction in non‐radiative recombination at the perovskite/electron transport layer interface. As a result, the inverted perovskite solar module (PSM) achieved a power conversion efficiency (PCE) of 22.08% with an aperture area of 11.1 cm2 (certified 21.58%), showing a low‐efficiency discrepancy versus the small‐area counterpart with an efficiency of 25.09%. Notably, the PSM can maintain 92.5% of its initial PCE after continuous 1000 h of 1‐sun operation at 65 °C in ambient air. [ABSTRACT FROM AUTHOR]

Stability and scalability have become the two main challenges for perovskite solar cells (PSCs) with the research focus in the field advancing toward commercialization. One of the prerequisites to solve these challenges is to develop a cost‐effective, uniform, and high quality electron transport layer that is compatible with stable PSCs. Sputtering deposition is widely employed for large area deposition of high quality thin films in the industry. Here the composition, structure, and electronic properties of room temperature sputtered SnO2 are systematically studied. Ar and O2 are used as the sputtering and reactive gas, respectively, and it is found that a highly oxidizing environment is essential for the formation of high quality SnO2 films. With the optimized structure, SnO2 films with high quality have been prepared. It is demonstrated that PSCs based on the sputtered SnO2 electron transport layer show an efficiency up to 20.2% (stabilized power output of 19.8%) and a T80 operational lifetime of 625 h. Furthermore, the uniform and thin sputtered SnO2 film with high conductivity is promising for large area solar modules, which show efficiencies over 12% with an aperture area of 22.8 cm2 fabricated on 5 × 5 cm2 substrates (geometry fill factor = 91%), and a T80 operational lifetime of 515 h. [ABSTRACT FROM AUTHOR]

• Sulfate ions are chemically adsorbed on TiO 2 surface via replacing hydroxyl groups. • Adsorption induced electron transfer impacts Fermi level and surface dipole of TiO 2. • Improved energy level alignments at interfaces are demonstrated. • Modified solar cells exhibit superior performance and stability. The photovoltaic performance of carbon-based CsPbI 2 Br solar cells is considerably limited by the quality of electron transporting layer (ETL)/perovskite interface. Specifically, the ETL/perovskite interface contains defects such as iodine vacancies. Meantime, the Fermi energy (E F) level of ETL is generally much higher than ones of perovskite and transparent conductive oxide (TCO) electrode. The above two issues together contribute to serious charge carrier recombination in devices. Oxyacid salts have been developed to be promising interfacial materials for ETL/perovskite interface, owing to their effective defect passivation and energy level tuning. However, the structure-functionality relationship of these materials has not been well established due to the unclear correlation between interfacial interaction and energy level tuning. Herein, through using CdSO 4 as modifier for TiO 2 ETL and controlling the thickness, we investigate the interfacial interaction and successfully correlates it to energy level tuning. It is shown that the chemically adsorbed SO 4 2- withdraws electrons from TiO 2. This interaction results in a downshifted E F level for TiO 2 and sets up a surface dipole moment which upshifts the energy band of perovskite. As a result, we obtain improved energy level alignment at both TCO/ETL interface and ETL/perovskite interface. The above effects lead to enhanced electron transport and mitigated charge carrier loss. Therefore, the power conversion efficiency of carbon-based CsPbI 2 Br solar cell is increased from 13.61 % to 15.09 %. Equally noteworthy is the remarkably enhanced environmental stability exhibited by these devices. [ABSTRACT FROM AUTHOR]