A Roadmap for Efficient and Stable All-Perovskite Tandem Solar Cells from a Chemistry Perspective

Abstract

Multijunction tandem solar cells offer a promising route to surpass the efficiency limit of single-junction solar cells. All-perovskite tandem solar cells are particularly attractive due to their high power conversion efficiency, now reaching 28% despite being made with relatively easy fabrication methods. In this review, we summarize the progress in all-perovskite tandem solar cells. We then discuss the scientific and engineering challenges associated with both absorbers and functional layers and offer strategies for improving the efficiency and stability of all-perovskite tandem solar cells from the perspective of chemistry.

A Universal Strategy of Perovskite Ink ‐ Substrate Interaction to Overcome the Poor Wettability of a Self‐Assembled Monolayer for Reproducible Perovskite Solar Cells

“…These different perovskite compositions have been widely studied because of their high device performance and the application potential in silicon‐perovskite and perovskite‐perovskite tandem cells, semi‐transparent photovoltaics, and indoor photovoltaics. [ 88–93 ] Figure shows the JV curves of devices employing MAPbI 3 , FA 1− x MA x PbI 3− y Br y , and MA‐free FA 1− x Cs x PbI 3− y Br y perovskites obtained by improving the perovskite ink–substrate interaction on Me‐4PACz SAM. The inset figure shows the photographic images of perovskite films obtained from DMF:DMSO and DMF:DMSO:NMP triple co‐solvent system.…”

“…These different perovskite compositions have been widely studied because of their high device performance and the application potential in silicon-perovskite and perovskite-perovskite tandem cells, semi-transparent photovoltaics, and indoor photovoltaics. [88][89][90][91][92][93] This highlights that a uniform perovskite layer of different compositions can be obtained with the perovskite ink-substrate interaction strategy. In addition to this, efforts were carried out to fabricate all-inorganic CsPbI 2 Br devices by adding NMP as a co-solvent.…”

Cationic and Anionic Vacancy Healing for Suppressed Halide Exchange and Phase Segregation in Perovskite Solar Cells

“…All-inorganic WBG cells, similar to their organic–inorganic hybrids with a high iodide/bromide content ratio, will undergo photoinduced halide phase segregation (PIHS) upon prolonged illumination. − Further, since the interconnecting layer that separates WBG and NBG cells is required to be ultrathin, the highly mobile halide ions are susceptible to halide ion exchange across layers and form undesired phases. − This process is generally referred to as an anion exchange reaction (AER) and originates because of a low thermodynamic barrier of mixing of bromide and iodide. , These processes are spontaneous and intrinsic to halide perovskites and are mediated by surface defects in perovskite nanocrystal (PNC) films and by bulk defects in annealed perovskite films. , Among all defect types, positively charged anion vacancies and negatively charged cation vacancies show relatively low formation energy, and passivating them can be a key solution to suppressing AER and PIHS. − …”

“…Nevertheless, concerns regarding their long-term stability can arise mainly as a result of WBG cell degradation caused by the use of organic–inorganic hybrid perovskites, the intrinsic instability of the iodide/bromide mixture, and the risk of metal diffusion or halide exchange across interconnected WBG/NBG cells. , The first concern can be addressed by avoiding an organic–inorganic hybrid and utilizing all-inorganic solar cells . However, the last two concerns regarding the intrinsic instability of I/Br mixtures and halide exchange are not trivial. , …”

Efficient All‐Perovskite Tandem Solar Cells with Low‐Optical‐Loss Carbazolyl Interconnecting Layers

“…Combining wide‐band gap (WBG) and narrow‐band gap (NBG) perovskites with interconnecting layers (ICLs) to construct monolithic all‐perovskite tandem solar cell is an effective way to achieve higher power conversion efficiency (PCE) than single‐junction solar cell, and has the potential to deliver practical PCEs over 30 % [1–4] . However, the PCE of all‐perovskite tandem solar cells has yet to surpass the expectation to date, [5,6] primarily due to the low photocurrent density realized in all‐perovskite tandem solar cells [7–11] .…”