Chemical passivation is an effective approach to suppress the grain surface dominated charge recombination in perovskite solar cells (PSCs). However, the passivation effect is usually labile on perovskite crystal surface since most passivating agents are weakly anchored. Here, the use of a bidentate molecule, 2‐mercaptopyridine (2‐MP), to increase anchoring strength for improving the passivation efficacy and stability synchronously is demonstrated. Compared to monodentate counterparts of pyridine and p‐toluenethiol, 2‐MP passivation on CH3NH3PbI3 film results in twofold improvement of photoluminescence lifetime and remarkably enhanced tolerance to chlorobenzene washing and vacuum heating, which improve the power conversion efficiency of n–i–p planar structured PSCs from 18.35% to 20.28%, with open‐circuit voltage approaching 1.18 V. Moreover, the CH3NH3PbI3 films passivated with 2‐MP exhibit unprecedented humid‐stability that they can be exposed to saturated humidity for at least 5 h, mainly due to the passivation induced surface deactivation, which renders the unencapsulated devices retaining 93% of the initial efficiency after 60 days aging in air with relative humidity of 60–70%.
The construction of state‐of‐the‐art hole‐transporting materials (HTMs) is challenging regarding the appropriate molecular configuration for simultaneously achieving high morphology uniformity and charge mobility, especially because of the lack of appropriate building blocks. Herein a semi‐locked tetrathienylethene (TTE) serves as a promising building block for HTMs by fine‐tuning molecular planarity. Upon incorporation of four triphenylamine groups, the resulting TTE represents the first hybrid orthogonal and planar conformation, thus leading to the desirable electronic and morphological properties in perovskite solar cells (PSCs). Owing to its high hole mobility, deep lying HOMO level, and excellent thin film quality, the dopant‐free TTE‐based PSCs exhibit a very promising efficiency of over 20 % with long‐term stability, achieving to date the best performances among dopant‐free HTM‐based planar n‐i‐p structured PSCs.
Molecular hole-transporting materials containing a weak electron acceptor core can simultaneously improve the stability and photovoltaic performance of perovskite solar cells.
All organic charge‐transporting layer (CTL)‐featured perovskite solar cells (PSCs) exhibit distinct advantages, but their scaling‐up remains a great challenge because the organic CTLs underneath the perovskite are too thin to achieve large‐area homogeneous layers by spin‐coating, and their hydrophobic nature further hinders the solution‐based fabrication of perovskite layer. Here, an unprecedented anchoring‐based coassembly (ACA) strategy is reported that involves a synergistic coadsorption of a hydrophilic ammonium salt CA‐Br with hole‐transporting triphenylamine derivatives to acquire scalable and wettable organic hole‐extraction monolayers for p–i–n structured PSCs. The ACA route not only enables ultrathin organic CTLs with high uniformity but also eliminates the nonwetting problem to facilitate large‐area perovskite films with 100% coverage. Moreover, incorporation of CA‐Br in the ACA strategy can distinctly guarantee a high quality of electronic connection via the cations' vacancy passivation. Consequently, a high power‐conversion‐efficiency (PCE) of 17.49% is achieved for p–i–n structured PSCs (1.02 cm2), and a module with an aperture area of 36 cm2 shows PCE of 12.67%, one of the best scaling‐up results among all‐organic CTL‐based PSCs. This work demonstrates that the ACA strategy can be a promising route to large‐area uniform interfacial layers as well as scaling‐up of perovskite solar cells.
Anchoring-based self-assembly (ASA) has emerged as a material-saving and highly scalable strategy to fabricate charge-transporting monolayers for perovskite solar cells (PSCs). However, the interfacial hole-extraction and electron-blocking performances are highly dependent on the compactness of the ASA monolayers, which has been largely ignored though it is very crucial to the efficiency and stability of PSCs. Here, strategically designed holetransporting molecules with different anchoring groups are incorporated to investigate the effect of bonding strength on monolayer quality and correlate these with the performance of p-i-n structured PSCs. It is unraveled that the anchoring groups with a stronger bonding strength are advantageous for improving the assembly rate, density, and compactness of ASA monolayer, thus enhancing charge collection and suppressing interfacial recombination. The prototypical PSCs based on optimal ASA monolayer achieve a high power conversion efficiency (PCE) of 21.43% (0.09 cm 2 ). More encouragingly, when enlarging the device area by tenfold, a comparable PCE of 20.09% (1.0 cm 2 ) can be obtained, suggesting that the ASA strategy is practically useful for scaling-up. The robust anchoring of the ASA monolayer also enhances devices stability, retaining 90% of initial PCE after three months. This study provides important insights into the ASA charge-transporting monolayers for efficient and stable PSCs.
The continuing efforts of creating novel D-A-π-A structured organic sensitizers with excellent optoelectronic properties have resulted in substantial improvement of power conversion efficiency (PCE) as well as stability of dye-sensitized solar cells (DSSCs). Here, we report a new molecular engineering strategy for enhancing optical gain and improving excited-state features in D-A-π-A structured organic sensitizers by improving the conjugation size and rigidity of the auxiliary acceptor functional group. A series of phenanthrene-fused-quinoxaline (PFQ)-based D-A-π-A organic sensitizers (WS-82, WS-83, and WS-84) are designed and synthesized for applications in DSSCs. Compared to 2,3-diphenylquinoxaline (DPQ)-based dye IQ-4, PFQ dyes show extended absorption spectra and improved open-circuit voltage performance. Upon a systematical engineering of alkyl chains and π-spacer structure, the unfavorable issues of PFQ dyes including low solubility and high energy barrier in intramolecular charge transition are successfully eliminated. When applied in iodine electrolyte-based DSSCs, the best performing PFQ dye WS-84 shows a PCE of 10.11%, which is much higher than that of our previous champion DPQ dye IQ-4 under the same conditions.
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