Aiming at stable CsPbI3 perovskite solar cells, Ge incorporated for the first time into DMAPbI3‐based precursor systems. Ge incorporation is found to be able to modify crystallization growth of CsPb1−xGexI3 films and reduce annealing temperature and treatment time by lowering CsPbI3 formation energy. The champion power conversion efficiency (PCE) of 19.52% is achieved with a certified PCE of 18.8%, which is the highest performance of CsPbI3 PSCs with alien element‐doping. In addition, in situ formation of GeO2 can passivate the grain boundary and surface defects, thus significantly improving the moisture resistance of the perovskite film and related devices. Excellent operational stability is achieved with no PCE degradation over 3000 h at a fixed bias voltage of 0.85 V under continuous white LED (6500 K) illumination and a nitrogen atmosphere. This work demonstrates that Ge‐incorporation is a promising way to stabilize CsPbI3 perovskite solar cells by simultaneously improving perovskite crystallinity and passivating the grain boundary and interfacial defects.

Ge Incorporation to Stabilize Efficient Inorganic CsPbI3 Perovskite Solar Cells

Recently, all-inorganic CsPbX3 perovskite solar cells have stimulated enormous research interests due to their numerous merits including superior thermal and light stability and become one of the most prominent research...

Crystallization Kinetics Modulation and Defects Suppression of All-Inorganic CsPbX3 Perovskite Film

CsPbI3 inorganic perovskites have attracted significant attention due to their desirable bandgap for tandem solar cells and excellent thermal stability. However, CsPbI3 perovskite solar cells (PSCs) still exhibit low efficiency and high energy loss due to nonradiative recombination. Herein, functionalized Ti3C2Fx quantum dots (QDs) are prepared and selected as interface passivators to enhance the performance of CsPbI3 PSCs. The systematic experimental results reveal that Ti3C2Fx QDs serve as effective passivators mainly in three aspects: 1) p‐type Ti3C2Fx QDs can tune the energy level of perovskite films and provide an efficient pathway for hole transfer; 2) Ti3C2Fx QDs can effectively passivate defects and reduce interfacial nonradiative recombination, and 3) Ti3C2Fx QDs form a barrier layer to prevent water invasion and improve the stability of CsPbI3 PSCs. Consequently, the champion CsPbI3 PSC with Ti3C2Fx QDs treatment exhibits an excellent efficiency of 20.44% with a high open‐circuit voltage of 1.22 V. Meanwhile, the corresponding device without encapsulation retained 93% of its initial efficiency after 600 h of storage in ambient air.

Fluorine Functionalized MXene QDs for Near‐Record‐Efficiency CsPbI3 Solar Cell with High Open‐Circuit Voltage

Inorganic CsPbI3 perovskite has shown great promise in highly stable perovskite solar cells due to the lack of volatile organic components. However, the inferior phase stability in ambient conditions resulted from the very small Cs+, limiting their practical applications. Here, CsPbI3-based 2D Ruddlesden-Popper (RP) perovskites were developed using two thiophene-based aromatic spacers, namely, 2-thiophenemethylamine hydroiodide (ThMA) and 2-thiopheneformamidine hydroiodide (ThFA), which significantly improved the phase stability by releasing the large inner stress of black-phase CsPbI3. The optimized ThFA-based 2D RP perovskite (n = 5, ThFA-Cs) device achieves a record efficiency of 16.00%. Importantly, the ThFA-Cs devices could maintain an average of 98% of their initial efficiencies after being stored in N2 at room temperature for 3000 h and 92% of their initial value at 80 °C for 960 h. This work provides a new perspective for exploration of the phase-stable CsPbI3-based perovskite with reduced dimensions for high-performance solar cells.

CsPbI3-Based Phase-Stable 2D Ruddlesden-Popper Perovskites for Efficient Solar Cells.

Inorganic cesium lead iodide perovskite CsPbI 3 is attracting great attention as a light absorber for single or multi-junction photovoltaics due to its outstanding thermal stability and proper bandgap. However, the device performance of CsPbI 3 -based perovskite solar cells (PSCs) is limited by the unsatisfactory crystal quality and thus severe non-radiative recombination. Here, vacuum-assisted thermal annealing (VATA) is demonstrated as an effective approach for controlling the morphology and crystallinity of the CsPbI 3  perovskite films formed from the precursors of PbI 2 , CsI, and dimethylammonium iodide (DMAI). By this method, a large-area and high-quality CsPbI 3 film is obtained exhibiting much reduce trap-state density with prolonged charge lifetime.  Consequently, the solar cell efficiency is raised from 17.26 to 20.06%, along with enhanced stability. The VATA would be an effective approach for fabricating high-performance thin-film CsPbI 3 perovskite optoelectronics.

Vacuum-Assisted Thermal Annealing of CsPbI3 for Highly Stable and Efficient Inorganic Perovskite Solar Cells.

Dynamic manipulation of crystallization is pivotal to the quality of polycrystalline films. A molten-salt-assisted crystallization (MSAC) strategy is presented to improve grain growth of the all-inorganic perovskite films. Compared with the traditional solvent annealing, MSAC enables more intensive mass transfer by means of convection and diffusion, which is beneficial to the interaction among the precursor colloids and to inducing in-plane growth of perovskite grains, resulting in the formation of high-quality perovskite films with suppressed pinhole and crack formation. Additionally, the introduction of molten salt alters the intermediate phases, and thus changes the crystallization pathways by reducing the energy barrier to produce films with desired optical and electrical properties. As a result, the MSAC strategy endows the devices with champion steady-state output efficiency of 19.83% and open-circuit voltage (Voc ) as high as 1.2 V, among the highest for this type of solar cell, thanks to its effectively reduced Voc deficit.

Ruijie Han

Papers

Molten-Salt-Assisted CsPbI3 Perovskite Crystallization for Nearly 20%-Efficiency Solar Cells