Hybrid metal-halide perovskite solar cells (PVSCs) have drawn unprecedented attention during the last decade due to their superior photovoltaic performance, facile and low-cost fabrication, and potential for roll-to-roll mass production and application for portable devices. Through collective composition, interface, and process engineering, a comprehensive understanding of the structure-property relationship and carrier dynamics of perovskites has been established to help achieve a very high certified power conversion efficiency (PCE) of 25.5%. Apart from material properties, the modified heterojunction design and device configuration evolution also play crucial roles in enhancing the efficiency. The adoption and/or modification of heterojunction structures have been demonstrated to effectively suppress the carrier recombination and potential losses in PVSCs. Moreover, the employment of multijunction structures has been shown to reduce thermalization losses, achieving a high PCE of 29.52% in perovskite/silicon tandem solar cells. Therefore, understanding the evolution of the device configuration of PVSCs from single junction, heterojunction to multijunction designs is helpful for the researchers in this field to further boost the PCE beyond 30%. Herein, we summarize the evolution and progress of the single junction, heterojunction and multijunction designs for high-performance PVSCs. A comprehensive review of the fundamentals and working principles of these designs is presented. We first introduce the basic working principles of single junction PVSCs and the intrinsic properties (such as crystallinity and defects) in perovskite films. Afterwards, the progress of diverse heterojunction designs and perovskite-based multijunction solar cells is synopsized and reviewed. Meanwhile, the challenges and strategies to further enhance the performance are also summarized. At the end, the perspectives on the future development of perovskite-based solar cells are provided. We hope this review can provide the readers with a quick catchup on this emerging solution-processable photovoltaic technology, which is currently at the transition stage towards commercialization.

Designs from single junctions, heterojunctions to multijunctions for high-performance perovskite solar cells.

The two-dimensional (2D)/three-dimensional (3D) heterojunction perovskite solar cell (PSC) has recently been recognized as a promising photovoltaic structure for achieving high efficiency and long-...

Tuning the Interfacial Dipole Moment of Spacer Cations for Charge Extraction in Efficient and Ultrastable Perovskite Solar Cells

Imidazole-Functionalized Imide Interlayers for High Performance Organic Solar Cells

In the journey to obtain well-crystallized mixed tin (Sn)–lead (Pb) iodide perovskite films for solar cell application, great difficulties have been presented due to very different crystallization rates between Sn- and Pb-based perovskite components. Herein, we report a new strategy to grow highly crystallized Sn–Pb perovskite (FA0.7MA0.3Sn0.5Pb0.5I3) for perovskite solar cells (PSCs). An iso-pentylammonium tetrafluoroborate ([PNA]BF4) ionic salt layer is introduced on top of poly(3,4-ethylenedioxythiophene)-poly-(styrenesulfonate) (PEDOT:PSS) to function as anchoring agent to bond Pb2+ to the surface of PEDOT:PSS, which can facilitate a quick crystallization of Pb-containing perovskite components and homogeneously distribute Sn/Pb elements inside the perovskite film in a vertical direction, uncovered by focused ion beam time-of-flight secondary ion mass spectrometry. Additionally, greatly reduced surface residual stress was also confirmed by X-ray diffraction. Lastly, these ionic salt molecules are able to encapsulate the acidic and hygroscopic surface of PEDOT:PSS to further ensure device stability. As a result, our strategies enabled a champion PCE of 20.11% for mixed Sn–Pb PSCs with improved thermal stability at 85 °C over 240 hours and shelf storage stability over 1200 hours. This work provides a new strategy to regulate the crystallization process of mixed Sn–Pb perovskites for both high performance and stability.

Balancing crystallization rate in a mixed Sn–Pb perovskite film for efficient and stable perovskite solar cells of more than 20% efficiency

Size mismatch induces cation segregation in CsPbI3: Forming energy level gradient and 3D/2D heterojunction promotes the efficiency of carbon-based perovskite solar cells to over 15%

Hole transporting materials (HTMs) play a crucial role in achieving highly efficient and stable perovskite solar cells (PSCs). Spiro-typed materials being the most widely used HTMs are commonly uti...

Design of Low Crystallinity Spiro-Typed Hole Transporting Material for Planar Perovskite Solar Cells to Achieve 21.76% Efficiency

The stacking of 2D perovskites on the top of 3D perovskites has been recognized as a promising interfacial treatment approach to improve the stability and efficiency of planar perovskite solar cells (PSCs). However, traditional 2D–3D perovskite heterojunctions obtained from the high-temperature annealing process still exhibit unsatisfactory charge transfer performance and interfacial voltage loss. Herein, we introduce isopentylammonium iodide (PNAI) as the large organic ammonium salt, and adjust the in situ grown processes of 2D perovskites by thermal treatments to form a multi-component capping layer composed of 2D perovskites with plenty of high n-value 2D phases (n ≥ 3, n is the number of inorganic layers) and residual PNAI molecules on 3D perovskites. Such an optimized composition for a 2D–3D perovskite heterojunction can remarkably improve the charge transfer performance, further suppress the interfacial ionic defects, and enlarge Fermi-level splitting, leading to a low bandgap-to-voltage loss (0.38 V). Consequently, this treatment strategy significantly improves the efficiency of planar PSCs to 22.62% with an outstanding open-circuit voltage of 1.16 V. Moreover, the unencapsulated PNAI-90 treated device stored under a relative humidity of 30 ± 5% for 1000 h still retains 89% of its initial PCE. This work offers a new strategy to construct a robust 2D–3D heterojunction for planar PSCs.

Yuankun Qiu

Papers

Design of Low Crystallinity Spiro-Typed Hole Transporting Material for Planar Perovskite Solar Cells to Achieve 21.76% Efficiency

Compositional optimization of a 2D–3D heterojunction interface for 22.6% efficient and stable planar perovskite solar cells

Tuning the Interfacial Dipole Moment of Spacer Cations for Charge Extraction in Efficient and Ultrastable Perovskite Solar Cells

Organic nanocrystals induced surface passivation towards high-efficiency and stable perovskite solar cells

Bottom Interfacial Engineering for Methylammonium-Free Regular-Structure Planar Perovskite Solar Cells Over 21%