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Perovskite material with a bandgap of 1.7–1.8 eV is highly desirable for the top cell in a tandem configuration with a lower bandgap bottom cell, such as a silicon cell. This can be achieved by alloying iodide and bromide anions, but light-induced phase-segregation phenomena are often observed in perovskite films of this kind, with implications for solar cell efficiency. Here, we investigate light-induced phase segregation inside quadruple-cation perovskite material in a complete cell structure and find that the magnitude of this phenomenon is dependent on the operating condition of the solar cell. Under short-circuit and even maximum power point conditions, phase segregation is found to be negligible compared to the magnitude of segregation under open-circuit conditions. In accordance with the finding, perovskite cells based on quadruple-cation perovskite with 1.73 eV bandgap retain 94% of the original efficiency after 12 h operation at the maximum power point, while the cell only retains 82% of the original efficiency after 12 h operation at the open-circuit condition. This result highlights the need to have standard methods including light/dark and bias condition for testing the stability of perovskite solar cells. Additionally, phase segregation is observed when the cell was forward biased at 1.2 V in the dark, which indicates that photoexcitation is not required to induce phase segregation.

Photoelectrolysis of water using solar energy into storable and environment-friendly chemical fuel in the form of hydrogen provides a potential solution to address the environmental concerns and fulfill future energy requirements in a sustainable manner. Achieving efficient and spontaneous hydrogen evolution in water using solar light as the only energy input is a highly desirable but a difficult target. In this work, we report perovskite solar cell integrated CdS-based photoanode for unbiased photoelectrochemical hydrogen evolution. An integrated tandem device consisting of mesoporous CdS/TiO2photoanode paired with a triple-cation perovskite (Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3) solar cell is developed via a facile fabrication route. The proposed photovoltaic integrated photoanode presents an efficient tandem configuration with high optical transparency to long-wavelength photons and strong photoelectrochemical conversions from short-wavelength photons. On the basis of this integrated tandem device, an unbiased photocurrent density of 7.8 mA/cm2is demonstrated under AM1.5G illumination.

Electron-extraction layer (EEL) plays a critical role in determining the charge extraction and the power conversion efficiencies of the organometal-halide perovskite solar cells (PSCs). In this work, Ti–Fe–O ternary oxides were first developed to work as an efficient EEL in planar PSC. Compared with the widely used TiOxand the pure FeOx, the ternary composites show superior properties in multiple aspects including the excellent stability of the precursor solution, good coverage on the substrates, outstanding electrical properties, and suitable energy levels. By varying the Fe content from 0 to 100% in the Ti–Fe–O composites, the conductivity of the resultant compact layer was markedly improved, confirmed by consistent results from the conductive atomic force microscopy and the linear sweep voltammetry measurements. Meanwhile, the compositional engineering tunes the energy level alignment of the Ti–Fe–O EEL/CH3NH3PbI3interface to a region that is favorable for obtaining excellent charge-extraction property. The combinational advantages of the Ti–Fe–O composites significantly improved the photovoltaic performance of the as-prepared solar cells. An increase of over 20% in the short-circuit current (JSC) density has been achieved due to a modified EEL conductivity and energy alignment with the perovskite layer. The reduction in the surface recombination and enhancement of the charge collection efficiency also result in about 15% increase in the fill factor. Notably, the device also showed remarkably alleviated hysteresis behavior, revealing a prominently inhibited surface recombination.

With rapid progress in recent years, organohalide perovskite solar cells (PSC) are promising candidates for a new generation of highly efficient thin-film photovoltaic technologies, for which up-scaling is an essential step toward commercialization. In this work, we propose a modified two-step method to deposit the CH3NH3PbI3(MAPbI3) perovskite film that improves the uniformity, photovoltaic performance, and repeatability of large-area perovskite solar cells. This method is based on the commonly used two-step method, with one additional process involving treating the perovskite film with concentrated methylammonium iodide (MAI) solution. This additional treatment is proved to be helpful for tailoring the residual PbI2level to an optimal range that is favorable for both optical absorption and inhibition of recombination. Scanning electron microscopy and photoluminescence image analysis further reveal that, compared to the standard two-step and one-step methods, this method is very robust for achieving uniform and pinhole-free large-area films. This is validated by the photovoltaic performance of the prototype devices with an active area of 1 cm2, where we achieved the champion efficiency of ∼14.5% and an average efficiency of ∼13.5%, with excellent reproducibility.