Halide Engineering for Mitigating Ion Migration and Defect States in Hot-Cast Perovskite Solar Cells

Abstract

Precise control of perovskite morphology to achieve large-sized grains with small-width grain boundaries is challenging and a pre-requisite for realizing high photovoltaic performance. Ion migration is another problem with perovskites, which hinders the device results. Herein, the incorporation of MABr into the mixed halide perovskite MAPbCl x I3–x has been carried out to minimize ion migration by replacing the mobile I– ions in the perovskite with Br–. Moreover, the introduction of MABr results in high-quality and smooth films with large grains of average size ∼45 μm. An increasing ratio of MABr was added in the perovskite precursor solution, and devices with the architecture FTO/PEDOT:PSS/Perovskite/PCBM/Rhodamine-101/Ag were fabricated using the hot-casting technique. The device with an MABr ratio of 0.1 (0.1MABr) showed a superior power conversion efficiency of >18% compared to ∼14% of the control without any MABr. For higher ratios, the performance deteriorated due to the increase in band gap of the perovskite, which resulted in the reduction of short-circuit current density. For 0.1MABr, minimum defect states and trap density were obtained using various experimental techniques, supporting its optimum device performance. Furthermore, minimum recombination loss took place in the 0.1MABr device. Similarly, the applicability of this technique in large-area devices was studied, and an efficiency of ∼17% was obtained, which is the highest in the literature for devices with 2.5 cm2 dimensions. These innovative concepts and approaches are vital tools to achieve large-area grains for increasing the solar cell performance for commercial applications.

Conjugated Polyelectrolyte-Passivated Stable Perovskite Solar Cells for Efficiency Beyond 20%

“…The PL intensity of the passivated film increased by almost three-fold in contrast to that of the pristine film due to the lesser nonradiative recombination originating from lower defect density. Moreover, the pristine film showed a slight blue shift from 770 to 765 nm after PHIA addition, signifying effective trap passivation. , For obtaining more insights into the carrier recombination mechanism, dark J – V measurements were carried out for the pristine and modified devices (Figure c). The reverse saturation current of the pristine device largely decreases after passivation, signifying lower carrier recombination and better charge transport.…”

“…After 40 h of heating, the passivated device retains ∼82% of its original PCE, whereas the pristine one degraded to ∼26% (Figure S8, Supporting Information). The reason for superior stability can be the minimized trap states as well as high-quality perovskite films with larger grains and reduced GBs. , The CPE also distributes along the GBs, which can enhance the hydrophobicity of the layer. This can be confirmed from the contact angle measurement performed with the pristine and passivated films (Figure a).…”

Ion Migration in Organic–Inorganic Hybrid Perovskite Solar Cells: Current Understanding and Perspectives

“…However, the pure MAPbI 3 or MAPbBr 3 showed no obvious changes after illumination. [ 74 ] Meanwhile, the splitting of XRD peaks was observed. It was suggested that the occurrence of this phenomenon could be attributed to the photo‐induced halide phase segregation, leading to one iodine‐poor phase and one iodine‐rich phase.…”

Additive-Assisted Defect Passivation for Minimization of Open-Circuit Voltage Loss and Improved Perovskite Solar Cell Performance

“…Promising optoelectronic properties including high absorption coefficient, suitable optical band edge, weak excitation binding energy, long carrier diffusion length, and long carrier lifetime have made hybrid organic–inorganic halide perovskites an attractive research topic in the last few years. − The certified power conversion efficiency (PCE) of perovskite solar cells (PSCs) has grown rapidly to more than 25% . This fast growth has become possible due to the extensive and insightful research, including material design, device engineering, interface modification, and development of different methods for perovskite preparation. − However, the perovskite films prepared using solution processing methods are polycrystalline and have noncoordinated ions as defects. These defects are majorly present at grain boundaries and on the surfaces of perovskite film, which work as recombination centers, hence greatly influencing the performance of PSCs. , Besides being harmful to device performance, these defects can also elevate the penetration of moisture and oxygen into perovskite and contribute significantly to the inherent instability of perovskite films and subsequently result in an unsatisfactory lifetime of PSCs under operating conditions. , Poor device stability is presently one of the most serious difficulties for commercialization of the PSCs.…”