Single-Crystal-Assisted In Situ Phase Reconstruction Enables Efficient and Stable 2D/3D Perovskite Solar Cells.

Perovskite solar cells (PSCs) that incorporate both two-dimensional (2D) and three-dimensional (3D) phases possess the potential to combine the high stability of 2D PSCs with the superior efficiency of 3D PSCs. Here, we demonstrated in situ phase reconstruction of 2D/3D perovskites using a 2D perovskite single-crystal-assisted method. A gradient phase distribution of 2D RP perovskites was formed after spin-coating a solution of the 2D Ruddlesden-Popper (RP) perovskite single crystal, (DFP)2PbI4, onto the 3D perovskite surface, followed by thermal annealing. The resulting film exhibits much reduced trap density, increased carrier mobility, and superior water resistance. As a result, the optimized 2D/3D PSCs achieved a champion efficiency of 24.87% with a high open-circuit voltage (VOC) of 1.185 V. This performance surpasses the control 3D perovskite device, which achieved an efficiency of 22.43% and a VOC of 1.129 V. Importantly, the unencapsulated device demonstrates significantly enhanced operational stability, preserving over 97% of its original efficiency after continuous light irradiation for 1500 h. Moreover, the extrapolated T80 lifetimes surpass 5700 h. These findings pave the way for rational regulation of the gradient phase distribution at the interface between 2D and 3D perovskites by employing 2D RP perovskite crystals to achieve stable and efficient PSCs.

Benzothieno[3,2-b]thiophene-Based Noncovalent Conformational Lock Achieves Perovskite Solar Cells with Efficiency over 24.

Organic semiconductors with noncovalently conformational locks (OSNCs) are promising building blocks for hole-transporting materials (HTMs). However, lack of satisfied neighboring building blocks negatively impacts the optoelectronic properties of OSNCs-based HTMs and imperils the stability of perovskite solar cells (PSCs). To address this limitation, we introduce the benzothieno[3,2-b]thiophene (BTT) to construct a new OSNC, and the resulting HTM ZS13 shows improved intermolecular charge extraction/transport properties, proper energy level, efficient surface passivation effect. Consequently, the champion devices based on doped ZS13 yield an efficiency of 24.39 % and 20.95 % for aperture areas of 0.1 and 1.01 cm2 , respectively. Furthermore, ZS13 shows good thermal stability and the capability of inhibiting I- ion migration, thus, leading to enhanced device stability. The success in neighboring-group engineering can triggered a strong interest in developing thienoacene-based OSNCs toward efficient and stable PSCs.

Inverted Wide-Bandgap 2D/3D Perovskite Solar Cells with >22% Efficiency and Low Voltage Loss.

Wide-bandgap perovskites play a key role in high-performance tandem solar cells, which have the potential to break the Schockley-Queisser limit. Here, a 2D/3D hybrid wide-bandgap perovskite was developed using octane-1,8-diaminium (ODA) as spacer. The incorporation of the ODA spacer can not only significantly reduce charge carrier nonradiative recombination loss but also inhibit phase separation. Moreover, with a synergy effect using butylammonium iodide (BAI) as a surface defect passivator, both the phase stability and device performance were further improved. Compared to the control inverted device with a VOC of 1.16 V and a PCE of 18.50%, the optimized PSCs based on a surface processed 2D/3D perovskite exhibit a superior high VOC of 1.26 V and a champion PCE of 22.19%, which is a record efficiency for wide-bandgap PSCs (Eg > 1.65 eV). This work provides a very effective strategy to suppress phase separation in wide-bandgap perovskites for highly efficient and stable solar cells.

Dimensional Tuning of Perylene Diimide-Based Polymers for Perovskite Solar Cells with Over 24% Efficiency.

The hygroscopic dopants used in Spiro-OMeTAD hole transport material (HTM) in state-of-the-art perovskite solar cells (PSCs) inevitably induce premature degradation of the devices. Here, two multifunctional polymer interface materials based on the perylene diimides (PDI) unit are developed. It is found that quasi-two-dimensional (2D) polymer 2DP-PDI can form a denser film and exhibit better hydrophobicity than linear polymer P-PDI. Importantly, 2DP-PDI can passivate the surface defects and extract hole carriers of perovskite film more effectively, leading to much reduced nonradiative recombination loss. With polymer interface material between the perovskite and HTM layers, the optimized device using 2DP-PDI and P-PDI yields a champion PCE of 24.20% and 23.09%, respectively, along with significantly improved stability, whereas the control device shows a lower efficiency of 22.23%. These results suggest that developing multifunctional polymer interface materials can be a promising strategy to improve the efficiency and stability of PSCs.

Incorporating of Lanthanides Ions into Perovskite Film for Efficient and Stable Perovskite Solar Cells.

Since Yan's work, incorporation of some lanthanide elements, such as Eu and Nd, into MAPbI3 layer has been proven to be a powerful strategy on improving the permanence of the perovskite solar cells (PSCs). However, a comprehensive configuration has not been given for different lanthanide elements doping while the mechanism has not been clarified. Herein, the incorporation of various lanthanides ions (Ln3+ = Ce3+ , Eu3+ , Nd3+ , Sm3+ , or Yb3+ ) into perovskite films to largely enhance the performance of PSCs is presented. Arising from the enlarged grain size and crystallinity of perovskite film upon Ln3+ ions doping, the efficiency and stability of PSCs are significantly improved. Extraordinarily, PSCs with Ce3+ doping achieve the best performance, with a champion power conversion efficiency (PCE) of 21.67% in contrast to 18.50% for pristine PSCs, and outstanding long-term and UV irradiation stability. Such high performance of PSCs after Ce3+ doping originates from special Ce3+ /Ce4+ redox pair and the unique 4f-5d absorption in the UV region. Finally, the flexible PSCs with low-temperature preparation are explored. Considering the richer deposition of cerium element in the earth and lower price, the findings may provide new opportunities for developing low-cost, highly efficient, air/UV stable, and flexible PSCs.

Dye Sensitization and Local Surface Plasmon Resonance-Enhanced Upconversion Luminescence for Efficient Perovskite Solar Cells.

Organic-inorganic hybrid perovskite solar cells (PSCs) have achieved rapid progress in this decade. However, the limited solar spectral utilization has restricted the further improvement of performance of the PSCs. One promising approach to solving this problem is utilizing IR to visible upconversion nanoparticles (UCNPs) in the PSC devices. Despite being confined by the lower quantum yield (QY) and smaller absorption cross section of the traditional UCNPs, their application is still a great challenge. In this work, the IR-783 dye-sensitized core/shell NaYF4:Yb3+, Er3+@NaYF4:Yb3+, and Nd3+ UCNPs were synthesized and coupled with plasmonic Au nanorods films. Thereby, the upconversion luminescence (UCL) intensity was enhanced by about 120-fold, whereas the luminescent QY was improved from 0.2 to 1.2%. Then, the composite UCNPs were assembled on the SnO2 layer of the PSCs, which resulted in the power conversion efficiency (PCE) increasing from 19.4 to 20.5% under simulated 100 mw/cm2 AM 1.5G irradiation. Up to now, it is the highest PCE for the PSCs based on various upconversion devices. Under the irradiation of a sun concentrator (1 W/cm2), the PCE of the device can be further improved to 21.1%. In-depth studies indicate that under standard sunlight irradiation, the improvement of PCE is due to both the IR to visible UCL and the scattering effect of the UCNPs. Under irradiation of a sun concentrator, the UCL contributes dominantly to the further improvement of PCE. This work provides an effective method for increasing the luminescent QY utilized in the PSCs and is of great significance for future PSCs that use sunlight concentrator.

Unraveling the Dual-Functional Mechanism of Light Absorption and Hole Transport of Cu2CdxZn1-xSnS4 for Achieving Efficient and Stable Perovskite Solar Cells.

Broadening the near-infrared (NIR) spectrum of device is critical to further improve the power conversion efficiency (PCE) of the perovskite solar cells (PSCs). In this work, novel Cu2CdZn1-xSnS4 (CZTS:Cd) film prepared by thermal evaporation method was employed as the NIR light-harvesting layer to complement the absorption of the perovskite. At the same time, Au nanorods (NRs) were introduced into the hole-transporting layer (HTL) to boost the utilization of CZTS:Cd to NIR light through localized surface plasmon effect. The perovskite/CZTS:Cd and Au NR-integrated PSCs can extend the photoelectric response to 900 nm. And more, the well-matched energy levels between CZTS:Cd and perovskite can effectively extract holes from perovskite and depress the charge carrier recombination. As a result, the champion PSC device insulating with CZTS:Cd and Au NRs demonstrates a remarkably increased PCE from 19.30 to 21.11%. The modified PSC devices also demonstrate highly improved long-time stability. The device retains a PCE of 87% after 500 h even under air with a relative humidity of 85%, implying the superior humidity stability of the devices with CZTS:Cd. This work suggests that perovskite/inorganic-integrated structure is a promising strategy to broaden and boost the NIR response of the PSCs.

High-Performance CsPbIBr2 Perovskite Solar Cells: Effectively Promoted Crystal Growth by Antisolvent and Organic Ion Strategies.

Growing attention has been paid to CsPbIBr2 perovskite solar cells (PSCs) after balancing the band gap and stability features of the interested full-inorganic perovskites. However, their power-conversion efficiency (PCE) still lags behind that of the PSCs using hybrid halide perovskite and how to increase the corresponding PCE is still a challenge. Herein, antisolvents and organic ion surface passivation strategies were systematically applied to precisely control the growth of CsPbIBr2 crystals for constructing a high-quality full-inorganic perovskite film. Through careful adjustments, a CsPbIBr2 film with a pure phase, full coverage, and high crystallinity with preferable (100) orientation was successfully obtained by introducing diethyl ether as the antisolvent followed by guanidinium surface passivation. The optimal CsPbIBr2 film was composed by a large grain with an average size of 950 nm, few grain boundaries, and higher hydrophobic property. Planer PSC using the optimal CsPbIBr2 film and electron-beam-deposited TiO2 compact layer exhibits a PCE of 9.17%, which ranks among the highest PCE range of the reported CsPbIBr2 PSCs. Besides, the designed CsPbIBr2 PSC exhibited good long-term stability, which could maintain 90% of the initial PCE in 40% humidity ambient, which remained constant after heat treatment at 100 °C for 100 h. Based on the optimal CsPbIBr2 film, the flexible and large-area (up to 225 mm2) PSCs were further fabricated. The adopted film improvement methods were further extended to other kinds of full-organic PSCs, which demonstrated the universality of this strategy.

Efficient rare earth co-doped TiO2 electron transport layer for high-performance perovskite solar cells.

Perovskite solar cells (PSCs) had received great attention as a result of their recent rapid increasing efficiency. However, the stability of PSCs is still a challenge due to the degradation of the perovskite layer caused by the high-energy ultraviolet (UV) irradiation. Inspired by the luminescent down converting ability for UV blocking and conversion as well as energy transfer between suitable rare earth (RE) ions, a planar CH3NH3PbI3 perovskite solar cell using Sm3+ and Eu3+ co-doped TiO2 electron transfer layer was designed. By optimizing the Sm3+ and Eu3+ doping concentration, the REs co-doped TiO2 ETL combines the advantages of high electron extraction and lower interfacial recombination caused by REs introduction, a power conversion efficiency of 19.01% was obtained. In addition, benefit from the enhanced ability to convert UV light into visible light of the co-doped ETL, the PSCs can sustain higher than at least 80% of the original efficiency over 25 days of full sunlight irradiation or after 100 h of UV illumination. Moreover, since the low-temperature pulsed laser deposition was adopted in ETL fabrication process, the large area (225 mm2) and flexibility devices were further explored, with PCEs of 12.60% and 15.48%, respectively. This work indicates that Sm3+ and Eu3+ co-doped ETLs are effective and promising method to enhance the photovoltaic performance and UV stability of PSCs, which can be further applied in other PSCs with different ETLs and co-doping types.