Electron states of perovskites nanocrystals and the future of solar cells (mini-review)

Perovskite materials such as formamidinium lead bromide (FAPbBr_(3 )) and ethylenediammonium-doped FAPbBr_(3 ) ({en}FAPbBr_(3 )) are widely utilized in nano-optoelectronic devices due to their relatively simple fabrication process, low cost, and high efficiency. Significant improvements have been achieved in theoretical and experimental studies of light emission and absorption, detection performance, and device design, especially for operation in the visible and near-infrared (NIR) regions. The possibilities of semiconductor perovskite solar cells (PSCs) as a reliable candidate for next-generation solar energy harvesting are considered. It was shown theoretically that in a nanosystem interacting with low-intensity radiation, the oscillator strengths of transitions, as well as the dipole moments of transitions for single-particle electron quantum-confined states emerging in perovskites containing FAPbBr_(3 ) and {en}FAPbBr_(3 ) nanocrystals (NCs), took on values significantly (by two orders of magnitude) exceeding the typical values of the corresponding quantities for semiconductors. It has been found that at the resonant frequency of the electron transition, the values of the maximum optical absorption of NCs, as well as the NC polarizability, assume giant values (seven orders of magnitude) higher than the values of these quantities at other frequencies. This makes it possible to use such nanosystems as strongly absorbing nanomaterials in a wide range of infrared (IR) waves with a wavelength that can be varied across a wide range depending on the type of contacting materials. Currently, new perovskite technologies are aiming to achieve the efficiency of crystalline silicon (Si). Compared to Si, PSCs have many advantages. Unlike Si, perovskites exhibit a direct bandgap, allowing for much more efficient absorption of light. As a result, only a thin film is required, reducing the cost of the manufacturing process (inexpensive solution processes). Unfortunately, a significant drawback is their sensitivity to moisture, air, and even light. Numerous research groups have experimented with various stabilization methods, but so far no PSC has demonstrated a durability close to that required for commercial solar cells (25 years). Instead of replacing Si, perovskite/Si tandem cells are expected to be the best solution. Because each material absorbs energy from different wavelengths of sunlight, perovskite/Si tandem cells have the potential to provide at least 20 % more energy efficiency than an Si cell. Tandem perovskite/Si photovoltaic cells have now achieved efficiencies of over 33 % in lab conditions, and their efficiency is much higher than that of Si and stand-alone cells.