Sujuan Wu

Coordination between urea and SnI ₂ promotes the redistribution of excess SnF ₂ toward the surface and grain boundaries, thereby suppressing Sn oxidation to enable efficient and stable tin-based perovskite solar cells.

Tin-based perovskites have been recognized as an optimal alternative to lead-based perovskites in the photovoltaic field due to their nontoxic nature and excellent optoelectrical properties. However, the efficiency and stability of tin-based perovskite solar cells (Sn-PSCs) as competing requirements are significantly worse than those of their lead-based counterparts, primarily due to the poor perovskite layer quality, Sn²⁺ oxidation, and high defect density. Herein, cyanamide (CA) with -C≡N and -NH₂ groups is introduced as a multifunctional additive to the precursor solution of Sn-PSCs to improve crystallinity and suppress microstructure defects. A series of characterizations demonstrates that the CA molecules have strong interactions with Sn²⁺ and I^-, thereby suppressing Sn²⁺ oxidation and migration of I^-. The CA additives result in reduced defect density and inhibit carrier recombination. Consequently, the Sn-PSCs modified by CA additives (CA-modified PSC) achieve a champion PCE of 11.74%, which is much higher than 7.32% of the control devices. Significantly, the exposure of unencapsulated CA-modified PSC to a N₂ atmosphere for 5000 h does not affect their initial efficiency, while the control devices show only 63% of their original efficiency. This work provides a straightforward and effective strategy for the development of efficient and stable Sn-PSCs.

Despite showing great potential in lead-free green energy, tin-based perovskite materials still face challenges such as inherent material instability and energy level misalignment with the hole transport layer (HTL), which limits the advancement of tin-based perovskite solar cells (Sn-PSCs). In this work, a natural antioxidant organic small molecule, thiolactic acid (TA), is used to modify the interface between PEDOT:PSS and the tin-based perovskite film. The TA molecule can cross-link to form a network polymer and regulate the microstructure and photoelectrical characteristics of PEDOT:PSS. Meanwhile, TA contains C═O and C─S groups, which can interact with Sn²⁺ to inhibit its oxidation. Moreover, the introduction of TA interfacial modification effectively improves the morphology of the perovskite film, suppresses interfacial charge recombination, and promotes carrier transport. Thus, TA-modified Sn-PSCs achieve a champion power conversion efficiency of 9.03%, surpassing 6.92% of the control PSCs. Even after being stored for 1000 h in a nitrogen atmosphere, the unencapsulated devices with TA modification still maintain 95.4% of their original PCE, compared to only 66.5% of the control devices. This study demonstrates the significance of the PEDOT:PSS/tin-perovskite interfacial modification on the efficiency and stability of Sn-PSCs.

The large voltage loss (V_loss) mainly stems from the mismatch between the perovskite film and electron transport layer in CsPbI₂Br-based all-inorganic perovskite solar cells (I-PSCs), which restricts the power conversion efficiency (PCE) of devices. To address this issue, potassium benzoate (BAP) is first introduced as a bifunctional passivation material to regulate the TiO₂/CsPbI₂Br interface, reduce the V_loss, and improve the photovoltaic performance of CsPbI₂Br-based I-PSCs. Eventually, the champion PCE of CsPbI₂Br-based I-PSCs without a hole transport layer modified by BAP (Target-PSCs) improves to 14.90% from the 12.14% of reference PSCs. The open-circuit voltage (V_oc) increases to 1.27 V from the initial 1.14 V after BAP modification. A series of characterizations show that BAP modification can not only optimize the energy level alignment of I-PSCs but also passivize the surface defects caused by uncoordinated Cs⁺/Pb²⁺. Moreover, the Target-PSCs without encapsulation demonstrate better thermal stability, which can maintain 107.6% of the original PCE after annealing at 160 °C for 140 min in humid air. While the reference PSCs only maintain 76.5% of their initial PCE after annealing at the same process. This work provides a simple strategy to modify the buried interface and improve the performance of CsPbI₂Br-based I-PSCs.

Due to the easy oxidation of Sn²⁺, which leads to form tin vacancy defects and poor perovskite film quality, caused by the rapid crystallization rate in tin-based perovskite solar cells (PSCs), their efficiency lags far behind that of lead-based PSCs. To improve the photovoltaic (PV) performance and stability of FA_0.9PEA_0.1SnI₃-based PSCs (T-PSCs), a small amount of Pb(SCN)₂ is introduced into a perovskite precursor as an antioxidant, and acetaminophen (ACE) with various functional groups is used to modify a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/perovskite interface. The results show that the Pb(SCN)₂ additive and ACE interfacial modification can not only optimize energy level alignment in T-PSCs but also inhibit Sn²⁺ oxidation to reduce the trap-state density, resulting in promoted carrier transport. The synergetic effect of the Pb(SCN)₂ antioxidant and ACE interfacial modification significantly reduces nonradiative recombination and improves the PV performance and stability of T-PSCs. Consequently, the unsealed T-PSCs with the Pb(SCN)₂ additive and ACE modification achieve a champion efficiency of 12.04% and maintain 99% of their initial PCE after being stored in N₂ for more than 2100 h, while reference T-PSCs demonstrate a champion PCE of 6.20% and retain only 72% of its initial PCE. Moreover, the modified T-PSCs without encapsulation demonstrate much better stability in humid air.

Serious open-circuit voltage (V_oc) loss originating from nonradiative recombination and mismatch energy level at TiO₂/perovskite buried interface dramatically limits the photovoltaic performance of all-inorganic CsPbI_xBr_3-x (x = 1, 2) perovskite solar cells (PSCs) fabricated through low-temperature methods. Here, an ionic liquid (IL) bridge is constructed by introducing 1-butyl-3-methylimidazolium acetate (BMIMAc) IL to treat the TiO₂/perovskite buried interface, bilaterally passivate defects and modulate energy alignment. Therefore, the V_oc of all-inorganic CsPbIBr₂ PSCs modified by BMIMAc (Target-1) significantly increases by 148 mV (from 1.213 to 1.361 V), resulting in the efficiency increasing to 10.30% from 7.87%. Unsealed Target-1 PSCs show outstanding long-term and thermal stability. During the accelerated degradation process (85 °C, RH: 50∼60%), the Target-1 PSCs achieve a champion PCE of 11.94% with a remarkable V_oc of 1.403 V, while the control PSC yields a promising PCE of 10.18% with a V_oc of 1.319 V. In particular, the V_oc of 1.403 V is the highest V_oc reported so far in carbon-electrode-based CsPbIBr₂ PSCs. Moreover, this strategy enables the modified all-inorganic CsPbI₂Br PSCs to achieve a V_oc of 1.295 V and a champion efficiency of 15.20%, which is close to the reported highest PCE of 15.48% for all-inorganic CsPbI₂Br PSCs prepared by a low-temperature process. This study provides a simple BMIMAc IL bridge to assist bifacial defect passivation and elevate the photovoltaic performance of all-inorganic CsPbI_xBr_3-x (x = 1, 2) PSCs.