Lewis-Acid Doping of Triphenylamine-Based Hole Transport Materials Improves the Performance and Stability of Perovskite Solar Cells

Metal-Free Catalytic Formation of a Donor-Acceptor-Donor Molecule and Its Lewis Acid-Adduct Singlet Diradical with High-Efficient NIR-II Photothermal Conversion

We have synthesized a quinone-incorporated bistriarylamine donor-acceptor-donor (D-A-D) semiconductor 1 by B(C6F5)3 (BCF) catalyzed C-H/C-H cross coupling via radical ion pair intermediates. Coordination of Lewis acids BCF and Al(ORF)3 (RF=C(CF3)3) to the semiconductor 1 afforded diradical zwitterions 2 and 3 by integer electron transfer. Upon binding to Lewis acids, the LUMO energy of 1 is significantly lowered and the band gap of the semiconductor is significantly narrowed from 1.93 eV (1) to 1.01 eV (2) and 1.06 eV (3). 2 and 3 are rare near-infrared (NIR) diradical dyes with broad absorption both centered around 1500 nm. By introducing a photo BCF generator, 2 can be generated by light-dependent control. Furthermore, the integer electron transfer process can also be reversibly regulated via the addition of CH3CN. In addition, the temperature of 2 sharply increased and reached as high as 110 °C in 10 s upon the irradiation of near-infrared-II (NIR-II) laser (1064 nm, 0.7 W cm-2), exhibiting a fast response to laser. It displays excellent photothermal stability with a photothermal (PT) conversion efficiency of 62.26 % and high-quality PT imaging.

Sequential Molecule-Doped Hole Conductor to Achieve >23% Perovskite Solar Cells with 3000-Hour Operational Stability

Although hole transport layers (HTLs) based on solution-processed doped Spiro-OMeTAD are extremely popular and effective for their remarkable performance in n-i-p perovskite solar cells (PSCs), their scalable application is still being held back by poor chemical stability and unsatisfied scalability. Essentially, the volatile components and hygroscopic nature of ionic salts often cause morphological deformation that deteriorate both device efficiency and stability. Herein, a simple and effective molecular implantation-assisted sequential doping (MISD) approach is strategically introduced to modulate spatial doping uniformity of organic films and fabricate all evaporated Spiro-OMeTAD layer in which phase-segregation free HTL is achieved accompanied with high molecular density, uniform doping composition, and superior optoelectronic characteristics. The resultant MISD-based devices attain a record power conversion efficiency (PCE) of 23.4%, which represents the highest reported value among all the PSCs with evaporated HTLs. Simultaneously, the unencapsulated devices realize considerably enhanced stability by maintaining over 90% of their initial PCEs in the air for 5200 h and after working at maximum power point under illumination for 3000 h. This method provides a facile way to fabricate robust and reliable HTLs toward developing efficient and stable perovskite solar cells.

Engineering Stable Lead-Free Tin Halide Perovskite Solar Cells: Lessons from Materials Chemistry

Substituting toxic lead with tin (Sn) in perovskite solar cells (PSCs) is the most promising route toward the development of high-efficiency lead-free devices. Despite the encouraging efficiencies of Sn-PSCs, they are still yet to surpass 15% and suffer detrimental oxidation of Sn(II) to Sn(IV). Since their first application in 2014, investigations into the properties of Sn-PSCs have contributed to a growing understanding of the mechanisms, both detrimental and complementary to their stability. This review summarizes the evolution of Sn-PSCs, including early developments to the latest state-of-the-art approaches benefitting the stability of devices. The degradation pathways associated with Sn-PSCs are first outlined, followed by describing how composition engineering (A, B site modifications), additive engineering (oxidation prevention), and interface engineering (passivation strategies) can be employed as different avenues to improve the stability of devices. The knowledge about these properties is also not limited to PSCs and also applicable to other types of devices now employing Sn-based perovskite absorber layers. A detailed analysis of the properties and materials chemistry reveals a clear set of design rules for the development of stable Sn-PSCs. Applying the design strategies highlighted in this review will be essential to further improve both the efficiency and stability of Sn-PSCs.

Enhanced Thermal Stability of Planar Perovskite Solar Cells Through Triphenylphosphine Interface Passivation

While extensive research has driven the rapid efficiency trajectory noted to date for organic-inorganic perovskite solar cells (PSCs), their thermal stability remains one of the key issues hindering their commercialization. Herein, a significant reduction in surface defects (a precursor to perovskite instability) could be attained by introducing triphenylphosphine (TPP), an effective Lewis base passivator, to the vulnerable perovskite/spiro-OMeTAD interface. Not only did TPP passivation enable a high power conversion efficiency (PCE) of 20.22 % to be achieved, these devices also exhibited superior ambient and thermal stability. Unlike the pristine device, which exhibited a sharp descend to 16 % of its initial PCE on storing in relative humidity of 10 %, at 85 °C for more than 720 h, the TPP-passivated devices retained 71 % of its initial PCE. Hence, this study presents a facile yet excellent approach to attain high-performing yet thermally stable PSCs.