Reconstructing the amorphous and defective surface for efficient and stable perovskite solar cells

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.

Automated summary

In this study, the researchers found that adding 4-tert-butylpyridine (tBP) to the hole transport layers of perovskite solar cells (PSCs) can recrystallize the amorphous and defective perovskite surface layers, leading to improved efficiency and stability of the devices. They also developed a more effective additive, 4-tert-butylpiperidine (tBPp), which exhibited stronger interaction with the perovskite surface defective sites. The optimized tBPp PSC achieved a champion efficiency of 24.2% and better operation stability.