Inverted planar perovskite solar cells with efficient and stability via optimized cathode-interfacial layer

Among the factors that lead to the reduction of the efficiency and stability of perovskite solar cells (PSCs) using [6,6] -phenyl C61 butyric acid methyl ester (PCBM) versus those of conventional structure, is the difficulty involved in realizing a high-quality film, and the non-radiative recombination that takes place at the interface between PCBM and perovskite. Our present work proposes a fabrication technique capable of overcoming these issues. Organic small molecule material was introduced along with PCBM, to obtain a homogeneously seamless film that plays the role of a dipole layer. The incorporated triethyl citrate (TEC) boosts the power conversion efficiency (PCE) from 14.56% to 17.86% with suppressed hysteresis, which originates primarily from the efficient electron transfer between the perovskite/PCBM and the Ag cathode interface. The results of electrochemical impedance spectroscopy measurements imply efficient electron transfer, low series resistance, and large recombination resistance in the photovoltaic device employing PCBM@TEC as the cathode interfacial layer. Specifically, the highly hydrophobic PCBM@TEC cathode interfacial layer (CIL) showed higher resistance to moisture, leading to a more environmentally-stable device. The results also showed the efficiency of the device retained 84% of its initial value after 30 days of operation under ambient conditions, which shows a visibly superior stability compared to a reference device that, under the same environment, retained only 37% its initial efficiency. Such advancement in the operational efficiency and stability of the device, will contribute to the longevity and cost-effectiveness of inverted PSC devices.