All-perovskite tandem solar cells with improved grain surface passivation

As a rising star of third-generation photovoltaic technology, organic–inorganic halide perovskite solar cells (PSCs) have exhibited high power conversion efficiency. However, the most investigated high-performance perovskites contain toxic lead, which may hinder their widespread applications. Among various alternative metal ions to replace lead for environmentally benign perovskites, tin has been successfully used in PSCs with the highest efficiency over 13% at present, making tin-based perovskites the most promising active materials for lead-free PSCs. In this review, we first summarize the device design of PSCs and the physical properties of tin-based perovskites. Then we state the major challenges for this field and discuss the essential techniques in film preparation. Specifically, tin rich conditions (tin halide) and suitable reducing agents are needed in the film preparation to prohibit Sn2+ oxidation, and solvent modulation is a feasible approach for controlling the film morphology. Meanwhile, chemical substitutions of A site and B site cations and X site anions to improve the optoelectronic properties of tin-based perovskites are comprehensively addressed. Moreover, tin–lead mixed perovskites that contain less lead than conventional perovskites for high-performance PSCs and tandem solar cells are discussed. This comprehensive review can shed light on the development of environmentally friendly PSCs and provide a guideline for realizing lead-free PSCs with high efficiency and stability via synergistic approaches.

Recent progress in tin-based perovskite solar cells

Perovskite solar cells (PSCs) emerging as a promising photovoltaic technology with high efficiency and low manufacturing cost have attracted the attention from all over the world. Both the efficiency and stability of PSCs have increased steadily in recent years, and the research on reducing lead leakage and developing eco-friendly lead-free perovskites pushes forward the commercialization of PSCs step by step. This review summarizes the main progress of PSCs in 2020 and 2021 from the aspects of efficiency, stability, perovskite-based tandem devices, and lead-free PSCs. Moreover, a brief discussion on the development of PSC modules and its challenges toward practical application is provided.

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The Main Progress of Perovskite Solar Cells in 2020-2021.

Over the past decade, metal halide perovskite photovoltaics have been a major focus of research, with single-junction perovskite solar cells evolving from an initial power conversion efficiency of 3.8% to reach 25.5%. The broad bandgap tunability of perovskites makes them versatile candidates as the subcell in a tandem photovoltaics architecture. Stacking photovoltaic absorbers with cascaded bandgaps in a multi-junction device can potentially overcome the Shockley–Queisser efficiency limit of 33.7% for single-junction solar cells. There is now intense activity in developing tandem solar cells that pair perovskite with either itself or with a variety of mature photovoltaic technologies such as silicon and Cu(In,Ga)(S,Se)2 (CIGS). In this review, we survey recent advances in the field and discuss its outlook. A discussion of the evolution, present status and future outlook for tandem solar cells employing perovskite materials.

Prospects for metal halide perovskite-based tandem solar cells

Efficient White Photoluminescence from Self-Trapped Excitons in Sb3+/Bi3+-Codoped Cs2NaInCl6 Double Perovskites with Tunable Dual-Emission

Monolithic all-perovskite tandem solar cells offer an avenue to increase power conversion efficiency beyond the limits of single-junction cells. It is an important priority to unite efficiency, uniformity and stability, yet this has proven challenging because of high trap density and ready oxidation in narrow-bandgap mixed lead–tin perovskite subcells. Here we report simultaneous enhancements in the efficiency, uniformity and stability of narrow-bandgap subcells using strongly reductive surface-anchoring zwitterionic molecules. The zwitterionic antioxidant inhibits Sn2+ oxidation and passivates defects at the grain surfaces in mixed lead–tin perovskite films, enabling an efficiency of 21.7% (certified 20.7%) for single-junction solar cells. We further obtain a certified efficiency of 24.2% in 1-cm2-area all-perovskite tandem cells and in-lab power conversion efficiencies of 25.6% and 21.4% for 0.049 cm2 and 12 cm2 devices, respectively. The encapsulated tandem devices retain 88% of their initial performance following 500 hours of operation at a device temperature of 54–60 °C under one-sun illumination in ambient conditions. Ensuring both stability and efficiency in mixed lead–tin perovskite solar cells is crucial to the development of all-perovskite tandems. Xiao et al. use an antioxidant zwitterionic molecule to suppress tin oxidation thus enabling large-area tandem cells with 24.2% efficiency and operational stability over 500 hours.

All-perovskite tandem solar cells with 24.2% certified efficiency and area over 1 cm2 using surface-anchoring zwitterionic antioxidant

Wide‐bandgap (WBG, ≈1.8 eV) perovskite is a crucial component to pair with narrow‐bandgap perovskite in low‐cost monolithic all‐perovskite tandem solar cells. However, the stability and efficiency of WBG perovskite solar cells (PSCs) are constrained by the light‐induced halide segregation and by the large photovoltage deficit. Here, a steric engineering to obtain high‐quality and photostable WBG perovskites (≈1.8 eV) suitable for all‐perovskite tandems is reported. By alloying dimethylammonium and chloride into the mixed‐cation mixed‐halide perovskites, wide bandgaps are obtained with much lower bromide contents while the lattice strain and trap densities are simultaneously minimized. The WBG PSCs exhibit considerably improved performance and photostability, retaining >90% of their initial efficiencies after 1000 h of operation at maximum power point. With the triple‐cation/triple‐halide WBG perovskites enabled by steric engineering, a stabilized power conversion efficiency of 26.0% in all‐perovskite tandem solar cells is further obtained. The strategy provides an avenue to fabricate efficient and stable WBG subcells for multijunction photovoltaic devices.

Steric Engineering Enables Efficient and Photostable Wide‐Bandgap Perovskites for All‐Perovskite Tandem Solar Cells

Thermally Stable All-Perovskite Tandem Solar Cells Fully Using Metal Oxide Charge Transport Layers and Tunnel Junction

Record Photocurrent Density over 26 mA cm−2 in Planar Perovskite Solar Cells Enabled by Antireflective Cascaded Electron Transport Layer

Abstract Bifacial monolithic all-perovskite tandem solar cells have the promise of delivering higher output power density by inheriting the advantages of both tandem and bifacial architectures simultaneously. Herein, we demonstrate, for the first time, the bifacial monolithic all-perovskite tandem solar cells and reveal their output power potential. The bifacial tandems are realized by replacing the rear metal electrodes of monofacial tandems with transparent conduction oxide electrodes. Bandgap engineering is deployed to achieve current matching under various rear illumination conditions. The bifacial tandems show a high output power density of 28.51 mW cm −2 under a realistic rear illumination (30 mW cm − 2 ). Further energy yield calculation shows substantial energy yield gain for bifacial tandems compared with the monofacial tandems under various ground albedo for different climatic conditions. This work provides a new device architecture for higher output power for all-perovskite tandem solar cells under real-world conditions. 

https://elight.springeropen.com/counter/pdf/10.1186/s43593-022-00028-w

Han Gao

Papers

All-perovskite tandem solar cells with 24.2% certified efficiency and area over 1 cm2 using surface-anchoring zwitterionic antioxidant

Steric Engineering Enables Efficient and Photostable Wide‐Bandgap Perovskites for All‐Perovskite Tandem Solar Cells

Thermally Stable All-Perovskite Tandem Solar Cells Fully Using Metal Oxide Charge Transport Layers and Tunnel Junction

Record Photocurrent Density over 26 mA cm−2 in Planar Perovskite Solar Cells Enabled by Antireflective Cascaded Electron Transport Layer

Revealing the output power potential of bifacial monolithic all-perovskite tandem solar cells