The critical role of grain boundaries for (CH(NH2)2PbI3)0.85(CH3NH3PbBr3)0.15 perovskite solar cells studied by Kelvin probe force microscopy under bias voltage and illumination is reported. Ion migration is enhanced at the grain boundaries. Under illumination, the light‐induced potential causes ion migration leading to a rearranged ion distribution. Such a distribution favors photogenerated charge‐carrier collection at the grain boundaries.

Beneficial effects are demonstrated by PbI2 incorporated into perovskite materials as a light absorber in solar cells. The PbI2 distributed into the perovskite layers leads to reduced hysteresis and ionic migration, and enables the fabrication of remarkably improved solar cells with a certified power conversion efficiency of 19.75% under air‐mass 1.5 global (AM 1.5G) illumination of 100 mW cm−2 intensity.

its rate reading is inevitably affected by the MAI sublimation during co-deposition.Another advantage of perovskite solar cells is the ability to tune the bandgap by mixing the halide anions. This applies to Cs mixed halide [ 18,19 ] as well as MA or FA lead mixed halides, enabling optimization of solar spectrum absorption for both single-junction and tandem solar cells.In this study, we report a dual source thermal evaporation process to deposit mixed halide CsPbIBr 2 perovskite absorber with a bandgap of 2.05 eV. This material has a potential to be used in a three-junction tandem as the quality of the material and therefore voltage of the device further improves. Inorganic CsI and PbBr 2 precursors are simultaneously evaporated onto a compact TiO 2 layer (c-TiO 2 ) on FTO glass substrates. Postannealing is carried out on a hot plate in a glove box to enable the full crystallization of the CsPbIBr 2 perovskite. A series of experiments investigating the effect of postanneal conditions on the crystalline structure is conducted in this work. Films achieve best quality in terms of crystallinity, thickness uniformity, and grain size uniformity when the samples are annealed at 250° for 10 min. Aiming at a simple architecture and an organiccomponent-free device, we fabricated a hole transport material (HTM) free planar Glass/FTO/c-TiO 2 /CsPbIBr 2 /Au solar cell, fi rst of its kind, with a PCE of 4.7%, a short-circuit current density ( J SC ) of 8.7 mA cm −2 , an open-circuit voltage ( V OC ) of 959 mV, and a fi ll factor (FF) of 56% under reverse scan, while PCE = 3.7%, J SC = 8.7 mA cm −2 , V OC = 818 mV and FF = 52% under forward scan.As described in the Experimental Section, the CsPbIBr 2 samples were prepared by evaporating the same molar quantity of CsI and PbBr 2 onto the substrates. The chemical composition of the samples was evaluated by X-ray photoelectron spectroscopy (XPS). The atomic ratio of Pb/Cs and Br/I was estimated to be 1.1 and 2.3, respectively, which is in good agreement with the CsPbIBr 2 composition. The XPS spectra are shown in Figure S1 in the Supporting Information. An Energy-dispersive X-ray spectroscopy (EDS) measurement at 15 kV was also carried out by a 20 µm line scan of the CsPbIBr 2 fi lm showing the atomic ratios of Pb/Cs and Br/I to be 1.2 and 1.94, respectively. The EDS spectra are shown in Figure S2 in the Supporting Information. One reason for the deviation between EDS and XPS results is the difference in accuracy between the measurements (XPS, ±5%, EDS, ±15%). It is also noted that the XPS carried out measures of the elemental composition of about 10 nm in depth from the surface. For bulk measurement, Ar ion etching will be required causing damage to the CsPbIBr 2 fi lm. Given the uniform column grains formed from the bottom to the surface of the CsPbIBr 2 fi lm as shown in Figure 5 a, The emergence of organic-inorganic hybrid halides perovskite solar cells has generated enormous interests in the photovoltaic research community. Due to their excellent optical absorption, good car...

Although perovskite solar cells have produced remarkable energy conversion efficiencies, they cannot become commercially viable without improvements in durability. We used gas chromatography–mass spectrometry (GC-MS) to reveal signature volatile products of the decomposition of organic hybrid perovskites under thermal stress. In addition, we were able to use GC-MS to confirm that a low-cost polymer/glass stack encapsulation is effective in suppressing such outgassing. Using such an encapsulation scheme, we produced multi-cation, multi-halide perovskite solar cells containing methylammonium that exceed the requirements of the International Electrotechnical Commission 61215:2016 standard by surviving more than 1800 hours of the Damp Heat test and 75 cycles of the Humidity Freeze test.

In this work, we report the benefits of incorporating p h e n e t h y l a m m o n i u m c a t i o n ( P E A + ) i n t o ( H C -(NH 2 ) 2 PbI 3 ) 0.85 (CH 3 NH 3 PbBr 3 ) 0.15 perovskite for the first time. After adding small amounts of PEA cation (<10%), the perovskite film morphology is changed but, most importantly, grain boundaries are passivated. This is supported by Kelvin Probe Force Microscopy (KPFM). The passivation results in the increase in photoluminescence intensity and carrier lifetimes of test structures and open-circuit voltages (V OC ) of the devices as long as the addition of PEA + is ≤4.5%. The presence of higher-band-gap quasi-2D PEA incorporated perovskite is responsible for the grain boundary passivation, and the quasi-2D perovskites are also found to be concentrated near the TiO 2 layer, revealed by PL spectroscopy. Results of moisture exposure tests show that PEA + incorporation is effective in slowing down the degradation of unencapsulated devices compared to the control devices without PEA + . These findings provide insights into the operation of perovskite solar cells when large cations are incorporated.

Cesium (Cs) metal halide perovskites for photovoltaics have gained research interest due to their better thermal stability compared to their organic−inorganic counterparts. However, demonstration of highly efficient Cs-based perovskite solar cells requires high annealing temperature, which limits their use in multijunction devices. In this work, low-temperatureprocessed cesium lead (Pb) halide perovskite solar cells are demonstrated. We have also successfully incorporated the less toxic strontium (Sr) at a low concentration that partially substitutes Pb in CsPb 1−x Sr x I 2 Br. The crystallinity, morphology, absorption, photoluminescence, and elemental composition of this low-temperature-processed CsPb 1−x Sr x I 2 Br are studied. It is found that the surface of the perovskite film is enriched with Sr, providing a passivating effect. At the optimal concentration (x = 0.02), a mesoscopic perovskite solar cell using CsPb 0.98 Sr 0.02 I 2 Br achieves a stabilized efficiency at 10.8%. This work shows the potential of inorganic perovskite, stimulating further development of this material.

The sensitivity of organic–inorganic perovskites to environmental factors remains a major barrier for these materials to become commercially viable for photovoltaic applications. In this work, the degradation of formamidinium lead iodide (FAPbI3) perovskite in a moist environment is systematically investigated. It is shown that the level of relative humidity (RH) is important for the onset of degradation processes. Below 30% RH, the black phase of the FAPbI3 perovskite shows excellent phase stability over 90 d. Once the RH reaches 50%, degradation of the FAPbI3 perovskite occurs rapidly. Results from a Kelvin probe force microscopy study reveal that the formation of nonperovskite phases initiates at the grain boundaries and the phase transition proceeds toward the grain interiors. Also, ion migration along the grain boundaries is greatly enhanced upon degradation. A post‐thermal treatment (PTT) that removes chemical residues at the grain boundaries which effectively slows the degradation process is developed. Finally, it is demonstrated that the PTT process improves the performance and stability of the final device.

We apply gas quenching to fabricate rubidium (Rb) incorporated perovskite films for high-efficiency perovskite solar cells achieving 20% power conversion efficiency on a 65 mm 2 device. Both double-cation and triple-cation perovskites containing a combination of methylammonium, formamidinium, cesium, and Rb have been investigated. It is found that Rb is not fully embedded in the perovskite lattice. However, a small incorporation of Rb leads to an improvement in the photovoltaic performance of the corresponding devices for both double-cation and triple-cation perovskite systems.