Dopant‐Free Pyrrolopyrrole‐Based (PPr) Polymeric Hole‐Transporting Materials for Efficient Tin‐Based Perovskite Solar Cells with Stability Over 6000 h

Abstract

A new set of pyrrolopyrrole‐based (PPr) polymers incorporated with thioalkylated/alkylated bithiophene (SBT/BT) is synthesized and explored as hole‐transporting materials (HTMs) for Sn‐based perovskite solar cells (TPSCs). Three bithiophenyl spacers bearing the thioalkylated hexyl (SBT‐6), thioalkylated tetradecyl (SBT‐14), and tetradecyl (BT‐14) chains are utilized to examine the effect of the alkyl chain lengths. Among them, the TPSCs are fabricated using PPr‐SBT‐14 as HTMs through a two‐step approach by attaining a power conversion efficiency (PCE) of 7.6% with a remarkable long‐term stability beyond 6000 h, which has not been reported elsewhere for a non‐PEDOT:PSS‐based TPSC. The PPr‐SBT‐14 device is stable under light irradiation for 5 h in air (50% relative humidity) at the maximum power point (MPP). The highly planar structure, strong intramolecular S(alkyl)···S(thiophene) interactions, and extended π‐conjugation of SBT enable the PPr‐SBT‐14 device to outperform the standard poly(3‐hexylthiophene,‐2,5‐diyl (P3HT) and other devices. The longer thio‐tetradecyl chain in SBT‐14 restricts molecular rotation and strongly affects the molecular conformation, solubility, and film wettability over other polymers. Thus, the present study makes a promising dopant‐free polymeric HTM model for the future design of highly efficient and stable TPSCs.

Highly Efficient HTM-Free Tin Perovskite Solar Cells with Outstanding Stability Exceeding 10000 h

“…TPSCs using 1% EDAI 2 as additive in a traditional one-step fabrication with PEDOT:PSS as an HTM tends to display an impressive enduring stability of over 2000 h upon storing inside a nitrogen-filled glovebox due to the slow surface passivation effect of the additive, 6 while the device fabricated using the two-step method has been reported to be stable for over 6000 h. 23 Hence, we expected our devices to display an enduring stability of at least about 4000 h upon shelf storage in a glovebox. Interestingly, the sm-ITO device displayed an outstanding stability when stored inside a nitrogen-filled glovebox (Figure 2e).…”

“…By fabricating a device using ITO-400, we obtained a very low PCE of 4.2% (Figure S11a), due to its poor J sc . We ascribe this to the absence of interfacial modifiers like conventional HTMs , or buffer layers like self-assembled monolayers, , which enable pinhole- and defect-free perovskite layer formation leading to enhanced photocurrent generation. Similarly, the impact of the ITO nanoparticle concentration was tested by doubling it to a concentration of 10 mg mL –1 .…”

“…Nevertheless, the incorporation of organic PTAA and PEAI would still lead to thermal stress after prolonged use . Hence, it becomes essential to develop stable alternative HTMs or a device without involving HTL. , …”

“…21 Nevertheless, the incorporation of organic PTAA and PEAI would still lead to thermal stress after prolonged use. 22 Hence, it becomes essential to develop stable alternative HTMs 23 or a device without involving HTL. 24,25 The first attempt to fabricate HTM-free TPSC yielded a low power conversion efficiency (PCE) of 3.7% as a result of inappropriate energy-band alignment of the perovskite with the ITO electrodes and poor film formation.…”

Surface and Interfacial Passivations for FASnI3 Solar Cells with Co-Cations

“…These cocationic approaches were performed according to a one-step fabrication procedure for which all tin perovskite precursors were added together in a solution to deposit on the hole-transport layer poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS) in one step. However, the reaction between SnI 2 and FAI/AI (A represents a cocation) was very rapid so that a two-step fabrication approach is favorable to retard the crystal growth rate. , We have recently demonstrated the application using the two-step method to deposit tin perovskite film on varied hole-transporting material (HTM) and self-assemble monolayer (SAM) surfaces with good device performance and stability. − In the present study, we systematically investigate a series of organic cations, MA, EA, AZ, DMA, HEA, IM, and GA (Figure a) on the A-site position to form cocations with FA in a FA x A 1– x SnI 3 (FA/A) solar cell using the two-step fabrication method in the presence of 20% SnF 2 and 1% EDAI 2 . The data of the top-view SEM (Figure S1), AFM (Figure S2), side-view SEM (Figure S3), XRD (Figure S4), UV–vis/PL spectra (Figure S5), UPS (Figure S6), TCSPC (Figure S7), EIS (Figure S8), GIWAXS (Figure S9), energy level diagram (Figure S10), and TOF-SIMS (Figure ) are shown to help with understanding of the device performance in relation to morphology, crystallinity, and optical and optoelectronic properties of this cocationic system.…”