Thienothiophene‐Assisted Property Optimization for Dopant‐Free π‐Conjugation Polymeric Hole Transport Material Achieving Over 23% Efficiency in Perovskite Solar Cells

Abstract

Hole transport materials (HTMs) play essential roles in achieving high photovoltaic performance and long‐term stability in the n–i–p structure of perovskite solar cell (PSC) devices. Recently, dopant‐free polymeric materials as HTMs in PSCs have attracted considerable attention owing to high carrier mobility and excellent hydrophobicity. However, achieving similar efficiencies to those of doped small molecule HTMs such as Spiro‐OMeTAD is a big challenge. Herein, a thienothiophene π‐bridge is selected as a stabilizer and energy level regulator incorporated into a donor–acceptor‐type HTM to synthesize a new polymer, Nap‐SiBTA. The incorporation of the thienothiophene group improves the thermal stability and favors the high planarity and face‐on orientation, promoting high charge carrier mobility and tunable optical band gap. Finally, the dopant‐free polymer Nap‐SiBTA‐based PSC achieves an excellent power conversion efficiency (PCE) of 23.07% with a high fill factor of 80.85%. To the best of the authors’ knowledge, this is one of the best efficiencies in dopant‐free HTM PSCs. Moreover, the unencapsulated device retains 93% of its initial PCE after 1000 h owing to the excellent hydrophobicity of Nap‐SiBTA. This work provides a general and practical method to design dopant‐free HTMs for the high efficiency and long‐term stability of PSCs.

Multifunctional Narrow Band Gap Terpolymer-Enabled High-Performance Dopant-Free Perovskite and Additive-Free Organic Solar Cells with Long-Term Stability

“…The decrease in the performance of TP-0.8-TEG over TP-0.8-EG is possibly due to the enhanced surface energies and decreased hydrophobicity, which rely on the degree of EG units and monomeric ratios. , Further, a dopant-free TP-0.8-EG-based PSC was compared to the dopant-free Spiro-OMeTAD-based control devices. Comparatively, the Spiro-OMeTAD devices displayed low V oc , J sc , and FF of 0.934 V, 24.65 mA cm –2 , and 72.3%, respectively, with a PCE of 16.64% in the reverse scan . In addition, the hysteresis index (HI) = (PCE R – PCE F )/PCE R for the dopant-free polymer-based PSCs was calculated.…”

“…Figure 5d discloses the stability graphs for new terpolymeric HTM perovskite devices monitored in an N 2 atmosphere for 1200 h. 19 The control polymer BT-UF showed a degradation rate of PCEs up to 59% for 1200 h. In comparison to BT-UF, our synthesized terpolymers showed improved stabilities. However, highly hygroscopic TP-0.8-EG terpolymers retained their initial PCE of 91% up to 800 h and that of 85% even up to 1200 h. However, TP-0.8-TEG holds only 65% of its original PCE up to 1200 h. "Furthermore, the device stability of the best-performed TP-0.8-EG-based PSCs has also been checked at 60 °C and under ambient air condition (25 °C, high humidity (RH): 90%) (Figure S26).…”

“…Comparatively, the Spiro-OMeTAD devices displayed low V oc , J sc , and FF of 0.934 V, 24.65 mA cm −2 , and 72.3%, respectively, with a PCE of 16.64% in the reverse scan. 19 In addition, the hysteresis index (HI) = (PCE R − PCE F )/PCE R for the dopant-free polymer-based PSCs was calculated. The HI of dopant-free Spiro-OMeTAD was 0.253, while that of dopant-free TP-0.8-EG was only 0.052.…”

“…As shown in Table 2, the reduced hysteresis index for the new BT polymer-based PSC could be credited to the charge carrier extraction and reduced charge recombination, most likely at the interface. 19,53 We further investigated external quantum efficiency (EQE) curves to estimate the integrated J sc values of the perovskite devices (Figure 2c). The integrated J sc values of TP-0.8-EGand TP-0.8-TEG-based perovskite devices are 24.90 and 24.20 mA cm −2 , respectively, which are in good agreement with the experimental J sc values of PSCs.…”

“…34,35 Meanwhile, the benzothiadiazole (BT) moiety, which consists of an ideal quinoid structure, is an ideal electron-withdrawing moiety for constructing A-π-D-type HTMs in PSCs, owing to its planar and rigid geometry. 19 However, the most pressing necessity at the current moment is to investigate a functionally enriched polymer advantageous for efficient and stable multifunctional devices. As discussed in our previous reports, a BT-BDT-based polymer with an alkoxynaphthyl side chain (P3) performed favorably for both PSCs (exhibited a PCE of 17.28%) and BHJ-OSCs (exhibited a PCE of 8.26%).…”