Ionic Liquid Bridge Assisting Bifacial Defect Passivation for Efficient All-Inorganic Perovskite Cells with High Open-Circuit Voltage.

Serious open-circuit voltage (Voc) loss originating from nonradiative recombination and mismatch energy level at TiO2/perovskite buried interface dramatically limits the photovoltaic performance of all-inorganic CsPbIxBr3-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 Voc 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 Voc of 1.403 V, while the control PSC yields a promising PCE of 10.18% with a Voc of 1.319 V. In particular, the Voc of 1.403 V is the highest Voc reported so far in carbon-electrode-based CsPbIBr2 PSCs. Moreover, this strategy enables the modified all-inorganic CsPbI2Br PSCs to achieve a Voc 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 CsPbIxBr3-x (x = 1, 2) PSCs.

Mutually Tuned Dual Additive Engineering Synergistically Enhances the Photovoltaic Performance of Tin-Based Perovskite Solar Cells.

Tin-based perovskite solar cells (T-PSCs) have become the star photovoltaic products in recent years due to their low environmental toxicity and superior photovoltaic performance. However, the easy oxidation of Sn2+ and the energy level mismatch between the perovskite film and charge transport layer limit its efficiency. In order to regulate the microstructure and photoelectric properties of tin-based perovskite films to enhance the efficiency and stability of T-PSCs, guanidinium bromide (GABr) and organic Lewis-based additive methylamine cyanate (MAOCN) are introduced into the FA0.9PEA0.1SnI3-based perovskite precursor. A series of characterizations show that the interactions between additive molecules and perovskite mutually reconcile to improve the photovoltaic performance of T-PSCs. The introduction of GABr can adjust the band gap of the perovskite film and energy level alignment of T-PSCs. They significantly increase the open-circuit voltage (Voc). The MAOCN material can form hydrogen bonds with SnI2 in the precursor, which can inhibit the oxidation of Sn2+ and significantly improve the short-circuit current density (Jsc). The synergistic modulation of the dual additives reduces the trap-state density and improves photovoltaic performance, resulting in an increased champion efficiency of 9.34 for 5.22% of the control PSCs. The unencapsulated T-PSCs with GABr and MAOCN dual additives prepared in the optimized process can retain more than 110% of their initial efficiency after aging for 1750 h in a nitrogen glovebox, but the control PSCs maintain only 50% of their initial efficiency kept in the same conditions. This work provides a new perspective to further improve the efficiency and stability of T-PSCs.

Significantly Improved Efficiency and Stability of Pure Tin-Based Perovskite Solar Cells with Bifunctional Molecules.

Tin-based perovskite solar cells (TPSCs) have become one of the most prospective photovoltaic materials due to their remarkable optoelectronic properties and relatively low toxicity. Nevertheless, the rapid crystallization of perovskites and the easy oxidization of Sn2+ to Sn4+ make it challenging to fabricate efficient TPSCs. In this work, a piperazine iodide (PI) material with -NH- and -NH2+- bifunctional groups is synthesized and introduced into the PEA0.1FA0.9SnI3-based precursor solution to tune the microstructure, charge transport, and stability of TPSCs. Compared with piperazine (PZ) containing only the -NH- group, the PI additive displays better effects on regulating the microstructure and crystallization, inhibiting Sn2+ oxidation and reducing trap states, resulting in an optimal efficiency of 10.33%. This is substantially better than that of the reference device (6.42%). Benefiting from the fact that PI containing -NH- and -NH2+- groups can passivate both positively charged defects and negatively charged halogen defects, unencapsulated TPSCs modified with the PI material can maintain about 90% of their original efficiency after being kept in a N2 atmosphere for 1000 h, much higher than the value of 47% in reference TPSCs without additives. This work provides a practical method to prepare efficient and stable pure TPSCs.