Dual-Strategy from a Single Molecule: Low-Cost, Dopant-Free, Stable D–A–D Type Quinoxaline-Based Hole-Transporting Materials for Perovskite Solar Cells in Both Indoor and Outdoor Applications

Abstract

Indoor photovoltaics represent a sustainable and reliable source of energy in low-power electronic devices, including the rapidly increasing Internet of Things (IoTs). In this context, hybrid perovskites have garnered surging attention as potential photovoltaic materials owing to their exceptional optoelectronic properties, appropriate band gaps, and ease of solution-based fabrication. Unfortunately, the high cost and necessity of hygroscopic dopants for hole-transporting materials (HTMs) such as spiro-OMeTAD is a major bottleneck, hindering the large-scale application of perovskite solar cells (PSCs). Considering the benefits of electron-deficient units in boosting the efficiency and stability of photovoltaic dyes and polymers, herein, we introduce two donor–acceptor–donor (D–A–D) quinoxaline-based HTMs, YN1 and YN2. These materials incorporate a D–A–D structure to strategically modulate HOMO levels, enhance stability, and reduce production costs. Differences in their photovoltaic performances were studied by using photoluminescence quenching, hole reorganization energy, hole mobility, and charge extraction capability. Dopant-free YN2-based PSCs deliver a maximum power conversion efficiency (PCE) of 28.35% at indoor photovoltaics (1000 lx LED illumination, 0.321 mW cm^–2) and 15.62% at outdoor conditions (AM 1.5G illumination, 100 mW cm^–2) which are at par with the gold-standard, doped spiro-OMeTAD. Compared to that, YN1-based devices show moderate efficiencies of 23.23% in indoor conditions and 10.92% in outdoor conditions. Interestingly, the YN2-based device outperforms YN1 and spiro-OMeTAD-based devices in long-term operational stability by maintaining 41.3% of initial PCE after 550 h of thermal stress at 85 °C with RH ∼ 55%. Alongside, due to the facile two-step synthesis process, the price of YN2 is only $35/g, which is cost-effective compared to commercially available high-performance reference HTMs. The economic viability, outstanding photovoltaic efficiency, and long-term stability of YN2 indicate its strong potential for future practical applications.