The performance of the blue perovskite light-emitting diodes (PeLEDs) is limited by the low photoluminescence quantum yields (PLQYs) and the unstable emission centers. In this work, we incorporate sodium bromide and acesulfame potassium into a quasi-2D perovskite to control the dimension distribution and promote the PLQYs. Benefiting from the efficient energy cascade channel and passivation, the sky-blue PeLED has an external quantum efficiency of 9.7% and no shift of the electroluminescence center under operation voltages from 4 to 8 V. Moreover, the half lifetime of the devices reaches 325 s, 3.3 times that of control devices without additives. This work provides new insights into enhancing the performance of blue PeLEDs.

The surfaces of perovskite solar cells (PSCs) are significant in determining the devices' efficiencies and stabilities. Here, we first uncover that the 4-tert-butylpyridine (tBP), as an essential additive in hole transport layers (HTLs), could recrystallize the amorphous and defective perovskite surface layers and passivate the defective sites on grain surfaces. The reconstruction induces a larger surface work function and mitigates the interface energy level misalignment between perovskite and HTLs, enlarging the photovoltage of the device. Then, we engineer the chemical bonding strength and develop a more effective HTL additive 4-tert-butylpiperidine (tBPp), which possesses a stronger interaction with perovskite surface defective sites than tBP. With the enhanced adsorption, the tBPp-reconstructed perovskite surface exhibits lower densities of defects and better stability under the stimuli of heat, light and humidity. As a result, the optimized tBPp PSC reaches a champion efficiency of 24.2% with much better operation stability. Tracked at the maximum power point under a continuous bias, the unsealed devices in a N 2 atmosphere can nearly maintain their initial efficiency after continuous light exposure for over 1200 h. Our findings provide an underlying understanding of the HTL additives, which markedly affect the efficiency and stability of n-i-p PSCs.

commercial silicon photovoltaic technology, which has achieved certified champion power conversion efficiency (PCE) of 25.7% in single-junction PSCs and 29.8% in tandem with silicon solar cells. [1,2] However, defects from the contact interfaces and the bulk in the polycrystalline perovskites films are the primary causes of carrier recombination loss and the instability of films and devices. [3][4][5] The chloride compounds are often used to enhance the performance by strengthening the film quality and eliminating defects. The better film quality is generally realized by controlling the crystallization process and grain size distribution, and stabilizing α-phase FAPbI 3 , respectively. For example, CH 3 NH 3 Cl (MACl) additive directs the growth to form intermediates for fabricating more stable perovskite and increasing the diffusion length to >1 µm. [6] A series of chloride compounds as additives or passivators were also introduced to lessen the defects. [7][8][9][10] To further understand the improvement mechanism, the spatial distribution of chloride compounds has been examined at different locations. The chloride of Cl-containing perovskite tended to be dispersed close to the perovskite/TiO 2 buried contact, according to the research from Starr and coworkers. [11] Pb-I anti-site deep-level defects at the Post-treatment is an essential passivation step for the state-of-the-art perovskite solar cells (PSCs) but the additional role is not yet exploited. In this work, perovskite film is fabricated under ambient air with wide humidity window and identify that chloride redistribution induced by post-treatment plays an important role in high performance. The chlorine/iodine ratio on the perovskite surface increases from 0.037 to 0.439 after cyclohexylmethylammonium iodide (CHMAI) treatment and the PSCs deliver a champion power conversion efficiency (PCE) of 24.42% (certificated 23.60%). The maximum external quantum efficiency of electroluminescence (EQE EL ) reaches to 10.84% with a radiance of 170 W sr −1 m −2 , forming the reciprocity relation between EQE EL and nonradiative open-circuit voltage loss (86.0 mV). After thermal annealing, 2D component of perovskite will increase while chloride decline, leading to improved photovoltage but reduced fill factor. Hence, it distinguishes that chloride enrichment can improve charge transport/ recombination simultaneously and 2D passivation can suppress the nonradiative recombination. Moreover, CHMAI can leverage their roles in charge transport/recombination for better performance than phenylethylammonium iodide (Cl/I = 0.114, PCE = 23.32%), due to the stronger binding energy of Cl − . This work provides the insight that the chloride fixation can improve the photovoltaic performance.

Defects passivation has been widely devoted to improving the performance of formamidinium lead triiodide (FAPbI3) perovskite solar cells; however, the effect of various defects on the α-phase stability is still unclear. Here, using density functional theory, we first reveal the degradation pathway of the FAPbI3 perovskite from α to δ phase and investigate the effect of various defects on the energy barrier of phase transition. The simulation results predict that iodine vacancies are most likely to trigger the degradation, since they obviously reduce the energy barrier of α-to-δ phase transition and have the lowest formation energies at the perovskite surface. A water-insoluble PbC2O4 compact layer was introduced on the perovskite surface to largely suppress the α-phase collapse through hindering the iodine migration and volatilization. Furthermore, this strategy largely reduced the interfacial nonradiative recombination and boosted the efficiency of the solar cells to 25.39% (certified 24.92%). Unpackaged device can maintain 92% of its initial efficiency after operation at maximum power point under simulated air mass 1.5G irradiation for 550 h.