Lifetime and Stability
Solar cells are getting better at converting light into electricity and expanding their working areas, but their stability and longevity are still not good enough for real-world use. Recent studies have focused on three key factors that help things stay stable over time: UV light, high temperatures, and water.
Early on in the creation of perovskite solar cells, it was found that UV light can make them less stable, especially when titanium oxide is used as the electron transport layer. When devices are introduced to and used with UV light, oxygen gaps appear in titanium oxide. This causes the devices to lose their efficiency quickly, with a drop in open-circuit voltage (Voc) and fill factor (FF). Recently, researchers have shown that adding trivalent cations like Al3+, Nd3+, and In3+ can stop oxygen gaps and make UV stability a lot better.
The chamber-passivated titanium oxide compact layer is much more stable in air, with less than 5% loss after tracking the highest power point for a long time. But it’s hard to completely stop oxygen gaps, and titanium oxide-based PSCs will always be unstable because of UV light. To make things stable, you could also use materials that don’t have many oxygen vacancies or where the oxygen vacancies don’t cause deep trap states. Recently, a material called BaSnO3 was used to study and create an electron transport layer for perovskite solar cells. These cells have much longer lives when they are fully lit up with visible and UV light.
Continuous light/dark cycle-induced perovskite device tiredness leads to performance loss. After dark ageing in an open circuit, a solar device’s performance drops to less than half of what it was at first. When it’s dark, lower temperatures make people much more tired. New study shows that the periodic movement of charge carriers creates flaws in the perovskite layer, leading to both interstitial spaces in the lattice and ionic gaps. It’s still not clear how this light/dark cycle affects the safety and performance of perovskite materials, but some perovskite solar devices get back to or even improve their original efficiency after dark ageing.
Lead Toxicity
Many people are very worried about the safety of perovskite solar cells because they contain lead, which makes them very inefficient and dangerous. Lead dissolves in water, which pollutes the environment and hurts both people and plants and animals. The people who work with photovoltaics are aware of the safety concerns and general worries about the technology. People can quickly and easily take lead salts, and kids are more likely to get sick because their gut systems are still growing.
Tin (Sn) and germanium (Ge), two group IV elements, have been used instead of lead (Pb) to solve this problem of toxicity. Lead-free perovskite solar cells that use tin-based perovskite devices have worked the best. Tin-based perovskite, on the other hand, is not as steady as lead-based ones because tin and germanium have higher energy states. Tin and germanium are also hard to use in stable and long-lasting perovskite solar devices because they easily change from the +2 state to the +4 state.
To make tin-based perovskite solar cells more efficient at turning light into electricity, the unstable problem needs to be fixed. This makes people want to make new materials that can fix problems with stability and toxins while keeping the interesting features of lead-based perovskite materials.
Hysteresis and Measurement Standards
People often study how hysteresis works in perovskite solar cells. It is found that flat devices exhibit more hysteresis than mesoporous devices. Most of the time, devices with metal oxide transport materials have higher hysteresis than devices with organic transport materials. Hysteresis happens less often in inverted perovskite solar cells that use organic charge transport materials, and mixed halide perovskite active materials can make it happen less often. The hysteresis behaviours in perovskite solar cells are caused by the stoichiometric ratios of the materials, their shape, the ferroelectric polarisation of inductive effects, the motion of ions within the materials, and bias-dependent traps at the surfaces. A lot of research has been done on things that have to do with hysteresis, like ion movement, ferroelectricity, and charge building. Even though perovskite materials are ferroelectric, the relative data make it less likely that ferroelectricity is the cause of hysteresis. Ionic reduction is likely to happen in the perovskite materials, which is likely to make hysteresis worse. To deal with this issue, realistic rules for testing perovskite solar devices need to be made. These rules should include how to report data from both forward and backward scanning direction measurements and how to keep the device at a fixed bias before measurements.
Large-Area and Flexible Devices
Perovskite materials are great for large-area, bendable devices because they don’t require a lot of energy to form or deposit. They also have low production costs and capital spending. These gadgets can be used for things like robotic flying vehicles and tools that you can wear. Scaling up perovskite solar cells is hard, though, because it’s not easy to keep making perovskite films without holes and selective charge carrier transport layers. Defects on the surface, in the mass, or at the interface can cause recombination centres to form, which lowers the open-circuit voltage, short-circuit current, and fill factor. It can be hard to make sure that all device layers can be made using low-temperature and printed methods on flexible materials that can be used for roll-to-roll printing. For big and bendy gadgets, different ways of making them have been thought of, like doctor-blading and printing, the direct contact intercalation method, electrode-position, and spray-coating. But because films and devices are so sensitive to small details in the manufacturing process, work needs to be done to make perovskite solar cells that work very well.
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