Dually‐Passivated Perovskite Solar Cells with Reduced Voltage Loss and Increased Super Oxide Resistance

Wide-Bandgap Perovskite Solar Cell Using a Fluoride-Assisted Surface Gradient Passivation Strategy

Wide-band gap (1.68 eV) perovskite solar cells (PSCs) are important components of perovskite/Si tandem devices. However, the efficiency of wide band gap PSCs has been limited by their huge open-circuit voltage (V_oc ) deficit due to non-radiative recombination. Deep-level acceptor defects are identified as the major killers of V_oc , and they can be effectively improved by passivation with ammonium salts. Theoretical calculation predicts that increasing the distance between F and -NH₃ ⁺ of fluorinated ammonium can dramatically enhance the electropositivity of -NH₃ ⁺ terminals, thus providing strong adsorption onto the negatively charged I_A and I_Pb anti-site defects. Characterizations further confirm that surface gradient passivation employing p-FPEAI demonstrates the most efficient passivation effect. Consequently, a record-efficiency of 21.63 % with the smallest V_oc deficit of 441 mV is achieved for 1.68 eV-band gap inverted PSCs. Additionally, a flexible PSC and 1 cm² opaque device also deliver the highest PCEs of 21.02 % and 19.31 %, respectively.

Deeper Insight into the Role of Organic Ammonium Cations in Reducing Surface Defects of the Perovskite Film

Organic ammonium salts (OASs) have been widely used to passivate perovskite defects. The passivation mechanism is usually attributed to coordination of OASs with unpaired lead or halide ions, yet ignoring their interaction with excess PbI₂ on the perovskite film. Herein, we demonstrate that OASs not only passivate defects by themselves, but also redistribute excess aggregated PbI₂ into a discontinuous layer, augmenting its passivation effect. Moreover, alkyl OAS is more powerful to disperse PbI₂ than a F-containing one, leading to better passivation and device efficiency because F atoms restrict the intercalation of OAS into PbI₂ layers. Inspired by this mechanism, exfoliated PbI₂ nanosheets are adopted to provide better dispersity of PbI₂ , further boosting the efficiency to 23.14 %. Our finding offers a distinctive understanding of the role of OASs in reducing perovskite defects, and a route to choosing an OAS passivator by considering substitution effects rather than by trial and error.

Thermal-Triggered Dynamic Disulfide Bond Self-Heals Inorganic Perovskite Solar Cells

One great challenge for perovskite solar cells (PSCs) lies in their poor operational stability under harsh stimuli by humidity, heat, light, etc . Herein, a thermal-triggered self-healing polyurethane (PU) is tailored to simultaneously improve the efficiency and stability of inorganic CsPbIBr 2 PSC. The dynamic covalent disulfide bonds between adjacent molecule chains in PU at high temperatures self-heal the in-service formed defects within CsPbIBr 2 perovskite film. Finally, the best device free of encapsulation achieves a champion efficiency up to 10.61% and an excellent long-term stability in air atmosphere over 80 days and persistent heat attack (85 o C) over 35 days. Moreover, the photovoltaic performances are recovered by a simple heat treatment.