Hole Transport Layer-Free Low-Bandgap Perovskite Solar Cells for Efficient All-Perovskite Tandems.

Low-bandgap (LBG, E g ∼1.25 eV) tin-lead (Sn-Pb) perovskite solar cells (PSCs) play critical roles in constructing efficient all-perovskite tandem solar cells (TSCs) that can surpass the efficiency limit of single-junction solar cells. However, the traditional poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole transport layer (HTL) in LBG PSCs usually restricts device efficiency and stability. Here, we report a strategy of employing 2-aminoethanesulfonic acid (i.e., taurine) as the interface bridge to fabricate efficient HTL-free LBG PSCs with improved optoelectronic properties of the perovskite absorbers at the buried contacts. Taurine-modified ITO substrate has lower optical losses, better energy level alignment, and higher charge transfer capability than PEDOT:PSS HTL, leading to significantly improved open-circuit voltage (V OC ) and short-circuit current density of corresponding devices. The best-performing LBG PSC with a power conversion efficiency (PCE) of 22.50% and an impressive V OC of 0.911 V has been realized, enabling all-perovskite TSCs with an efficiency of 26.03%. The taurine-based HTL-free TSCs have highly increased stability, retaining more than 90% and 80% of their initial PCEs after constant operation under 1-sun illumination for 600 h and under 55 °C thermal stress for 950 h, respectively. This work provides a facile strategy for fabricating efficient and stable perovskite devices with a simplified HTL-free architecture. This article is protected by copyright. All rights reserved.