Stable pure-iodide wide-band-gap perovskites for efficient Si tandem cells via kinetically controlled phase evolution

Recent progress in perovskite solar cells: from device to commercialization

Formamidinium (FA)-rich lead iodide perovskite solar cells (PSCs) are gaining popularity because of their excellent photovoltaic performance. Nevertheless, the FA-rich perovskites processed by a two-step sequential deposition method usually possess...

Modulation of Nucleation and Crystallization in PbI2 Films Promoting Preferential Perovskite Orientation Growth for Efficient Solar Cells

Judicious tailoring of the interface between the SnO2 electron‐transport layer and the perovskite buried surface plays a pivotal role in obtaining highly efficient and stable perovskite solar cells (PSCs). Herein, a DL‐carnitine hydrochloride (DL) is incorporated into the perovskite/SnO2 interface to suppress the defect‐states density. A DL‐dimer is obtained at the interface by an intermolecular esterification reaction. For the SnO2 film, the Cl− in the DL‐dimer can passivate oxygen vacancies (VO) through electrostatic coupling, while the N in the DL‐dimer can coordinate with the Sn4+ to passivate Sn‐related defects. For the perovskite film, the DL‐dimer can passivate FA+ defects via hydrogen bonding and Pb‐related defects more efficiently than the DL monomer. Upon DL‐dimer modification, the interfacial defects are effectively passivated and the quality of the resultant perovskite film is improved. As a result, the DL‐treated device achieves a gratifying open‐circuit voltage (VOC) of 1.20 V and a champion power conversion efficiency (PCE) of 25.24%, which is a record value among all the reported FACsPbI3 PSCs to date. In addition, the unencapsulated devices exhibit a charming stability, sustaining 99.20% and 90.00% of their initial PCEs after aging in air for 1200 h and continuously operating at the maximum power point tracking for 500 h, respectively.

25.24%‐Efficiency FACsPbI3 Perovskite Solar Cells Enabled by Intermolecular Esterification Reaction of DL‐Carnitine Hydrochloride

Although CsPbI3 perovskites have shown tremendous potential in the photovoltaic field owing to their excellent thermal stability, the device performance is seriously restricted by severe photovoltage loss. The buried titanium oxide/perovskite interface plays a critical role in interfacial charge transport and perovskite crystallization, which is closely related to open‐circuit voltage deficit stemming from nonradiative recombination. Herein, target molecules named 3‐sulphonatopropyl acrylate potassium salts are deliberately employed with special functional groups for modifying the buried interface, giving rise to favorable functions in terms of passivating interfacial defects, optimizing energetic alignment, and facilitating perovskite crystallization. Experimental characterizations and theoretical calculations reveal that the buried interface modification inhibits the electron transfer barrier and simultaneously improves perovskite crystal quality, thereby reducing trap‐assisted charge recombination and interfacial energetic loss. Consequently, the omnibearing modification regarding the buried interface endows the devices with an impressive efficiency of 20.98%, achieving a record‐low VOC deficit of 0.451 V. The as‐proposed buried interface modification strategy renders with a universal prescription to push the limit of VOC deficit, showing a promising future in developing high‐performance all‐inorganic perovskite photovoltaics.

Pushing the Limit of Open‐Circuit Voltage Deficit via Modifying Buried Interface in CsPbI3 Perovskite Solar Cells

Black‐phase formamidinium lead iodide (FAPbI3) with narrow bandgap and high thermal stability has emerged as the most promising candidate for highly efficient and stable perovskite photovoltaics. In order to overcome the intrinsic difficulty of black‐phase crystallization and to eliminate the lead iodide (PbI2) residue, most sequential deposition methods of FAPbI3‐based perovskite will introduce external ions like methylammonium (MA+), cesium (Cs+), and bromide (Br–) ions to the perovskite structure. Here a zwitterion‐functionalized tin(IV) oxide (SnO2) is introduced as the electron‐transport layer (ETL) to induce the crystallization of high‐quality black‐phase FAPbI3. The SnO2 ETL treated with the zwitterion of formamidine sulfinic acid (FSA) can help rearrange the stack direction, orientation, and distribution of residual PbI2 in the perovskite layer, which reduces the side effect of the residual PbI2. Besides, the FSA functionalization also modifies SnO2 ETL to suppress deep‐level defects at the perovskite/SnO2 interface. As a result, the FSA–FAPbI3‐based perovskite solar cells (PSCs) exhibit an excellent power conversion efficiency of up to 24.1% with 1000 h long‐term operational stability. These findings provide a new interface engineering strategy on the sequential fabrication of black‐phase FAPbI3 PSCs with improved optoelectronic performance.

Zwitterion‐Functionalized SnO2 Substrate Induced Sequential Deposition of Black‐Phase FAPbI3 with Rearranged PbI2 Residue

Abstract Although pure formamidinium iodide perovskite (FAPbI3) possesses an optimal gap for photovoltaics, their poor phase stability limits the long-term operational stability of the devices. A promising approach to enhance their phase stability is to incorporate cesium into FAPbI3. However, state-of-the-art formamidinium–cesium (FA–Cs) iodide perovskites demonstrate much worse efficiency compared with FAPbI3, limited by the different crystallization dynamics of formamidinium and cesium, which result in poor composition homogeneity and high trap densities. We develop a novel strategy of crystallization decoupling processes of formamidinium and cesium via a sequential cesium incorporation approach. As such, we obtain highly reproducible, highly efficient and stable solar cells based on FA1–xCsxPbI3 (x = 0.05–0.16) films with uniform composition distribution in the nanoscale and low defect densities. We also revealed a new stabilization mechanism for Cs doping to stabilize FAPbI3, i.e. the incorporation of Cs into FAPbI3 significantly reduces the electron–phonon coupling strength to suppress ionic migration, thereby improving the stability of FA–Cs-based devices.

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Decoupling engineering of formamidinium–cesium perovskites for efficient photovoltaics

Perovskite photovoltaics with the advantages of facile fabrication and high efficiency have been the rising star in the field for a decade. Methylammonium lead triiodide (MAPbI3) was the first widely studied perovskite to initiate the boom of perovskite photovoltaics, but it was later considered thermodynamically instable for commercialization. Here, we demonstrate that simple cesium (Cs) doping without any complicated process can form a stable MA-based perovskite with a widened bandgap, which may broaden the application of MA-based perovskites in tandem solar cells. A record-high efficiency of ≤22% is thus achieved for a 1.6 eV bandgap perovskite solar cell. This work not only provides a new stable and efficient pure iodide candidate as a 1.6 eV bandgap perovskite but also reveals that Cs incorporation can help improve the efficiency and stability of MA-based perovskites.

Stable Pure Iodide MA0.95Cs0.05PbI3 Perovskite toward Efficient 1.6 eV Bandgap Photovoltaics.

Abstract Perovskite solar cells (PSCs) have undergone a dramatic increase in laboratory-scale efficiency to more than 25%, which is comparable to Si-based single-junction solar cell efficiency. However, the efficiency of PSCs drops from laboratory-scale to large-scale perovskite solar modules (PSMs) because of the poor quality of perovskite films, and the increased resistance of large-area PSMs obstructs practical PSC applications. An in-depth understanding of the fabricating processes is vital for precisely controlling the quality of large-area perovskite films, and a suitable structural design for PSMs plays an important role in minimizing energy loss. In this review, we discuss several solution-based deposition techniques for large-area perovskite films and the effects of operating conditions on the films. Furthermore, different structural designs for PSMs are presented, including the processing technologies and device architectures. 

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Zhixiao Qin

Papers

Zwitterion‐Functionalized SnO2 Substrate Induced Sequential Deposition of Black‐Phase FAPbI3 with Rearranged PbI2 Residue

Decoupling engineering of formamidinium–cesium perovskites for efficient photovoltaics

Stable Pure Iodide MA0.95Cs0.05PbI3 Perovskite toward Efficient 1.6 eV Bandgap Photovoltaics.

Recent Progress in Large-Area Perovskite Photovoltaic Modules

Activating photocatalytic hydrogen generation on inorganic lead-free Cs2AgBiBr6 perovskite via reversible Cu2+/Cu+ redox couple