Design of Low Crystallinity Spiro-Typed Hole Transporting Material for Planar Perovskite Solar Cells to Achieve 21.76% Efficiency

Abstract

Hole transporting materials (HTMs) play a crucial role in achieving highly efficient and stable perovskite solar cells (PSCs). Spirotyped materials being the most widely used HTMs are commonly utilized with dopants, such as Li-TFSI, to improve their carrier mobility significantly. However, dopants could affect the morphology of hole transporting layer negatively by forming defects and pinholes which restrict the performance of devices. Here, we adopt the extended πconjugated structures N-ethylcarbazole and dibenzothiophene to substitute the donor group 4-methoxyphenyl of spiro-OMeTAD, devising two novel HTMs, SC and ST, respectively. Notably, SC possesses low crystallinity and good solubility due to the existence of ethyl in side groups, leading to decent miscibility with Li-TFSI to prevent unfavorable phase-separation. The SC-based device delivers the best power conversion efficiency (PCE) of 21.76% which is higher than that of spiro-OMeTAD (20.73%), attributed to the formation of smooth and pinhole-free morphology. Moreover, it exhibits long-term stability and retains over 90% of initial PCE value for more than 30 days without encapsulation in ambient air. In contrast, the STbased device suffers from dense pinholes induced by its relatively high crystallinity and poor solubility, resulting in a low PCE of 18.18% and inferior stability. Thus, it is effective to modify the side groups in spiro-typed HTMs with specific structures to obtain predictable properties, fabricating PSCs with high efficiency and stability facilely.

Surface‐Anchored Acetylcholine Regulates Band‐Edge States and Suppresses Ion Migration in a 21%‐Efficient Quadruple‐Cation Perovskite Solar Cell

“…The highest occupied molecular orbital of Spiro‐OMeTAD is −5.22 eV. [ 59 ] Thus, better alignment of the band would exist at the interface between the AChCl‐treated OIHP and Spiro‐OMeTAD (Figure S10, Supporting Information). This superior alignment has the potential to accelerate the transportation of holes at the interface.…”

Improving the Long‐Term Stability of Doped Spiro‐Type Hole‐Transporting Materials in Planar Perovskite Solar Cells

“…This negative effect has been mitigated using the tools offered by organic chemistry for the meticulous design and synthesis of alternative dopantfree HTMs including from polymeric materials, which have demonstrated good hole-transport ability for the preparation of highly efficient PSCs, [34,35] to small organic molecules based on different types of structures. [36][37][38][39] Notwithstanding, previous works have shown that doped HTMs can also show remarkable long-term stabilities, maintaining, in some cases, 90% of their initial efficiency after more than 30 days or even under continuous illumination, which demonstrates that the presence of dopants is not incompatible with long-term stable PSCs. [36,40] Herein, we report the synthesis and the optoelectronic characterization of two new asymmetric spiro-based HTMs that incorporate phenoxazine or phenothiazine units in a diphenylamino-substituted fluorene scaffold.…”

“…[36][37][38][39] Notwithstanding, previous works have shown that doped HTMs can also show remarkable long-term stabilities, maintaining, in some cases, 90% of their initial efficiency after more than 30 days or even under continuous illumination, which demonstrates that the presence of dopants is not incompatible with long-term stable PSCs. [36,40] Herein, we report the synthesis and the optoelectronic characterization of two new asymmetric spiro-based HTMs that incorporate phenoxazine or phenothiazine units in a diphenylamino-substituted fluorene scaffold. Phenoxazine (POZ) and phenothiazine (PTZ) are well-known heterocyclic structures that consist of two benzene rings fused through a 1,4-oxazine or 1,4-thiazine, respectively, rendering a butterfly-shaped structure which exhibits remarkable properties for multiple fields.…”

Green‐Chemistry‐Inspired Synthesis of Cyclobutane‐Based Hole‐Selective Materials for Highly Efficient Perovskite Solar Cells and Modules

“…[15][16][17][18][19][20] To date, 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD) dominates the field and despite its high price is routinely used as the gold standard for the As of the success of spiro-OMeTAD,m any research groups have been focused on spiro-type compounds,e xpecting to improve the PCE with slight structural modifications. [22,23] Several groups studied central 9,9'-spirobifluorenelinked HTMs including dimethylfluorenyl-, ethylcarbazolyl-, and fluorinated methoxyphenyl-terminated examples recently reported by Seo, [24] Chen, [25] and Yang, [26] respectively,a s well as the development of new central spiro-cored structures such as spiro[fluorene-9,9'-xanthene], [27][28][29][30][31] spirobisacridine, [32] thiophene-containing spiro cores [33][34][35] and other spiro-type derivatives. [36,37] However,t he synthesis of such spiro-type compounds typically requires am ulti-step reaction scheme involving low temperature (À78 8 8C), sensitive (n-butyllithium), and aggressive (Br 2 )reagents resulting in arelative high material cost, consequently leading to as ignificant contribution to the total device cost and non-negligible environmental impact.…”