No abstract

Despite the fact that power conversion efficiency (PCE) has been greatly improved in recent years, perovskite solar cells (PSCs) need to overcome some challenges, like stability, for the commercial application. Herein, an anionic conjugated polyelectrolyte, sulfonic-containing polyfluorene (abbreviated to SPF), has been developed to modify the interface between the electron-transporting layer (ETL) SnO2 and the optoelectronic active layer MAPbI3 in the n-i-p cells. After 40 days of storage in atmospheric environment in the dark with exposure to a controlled humidity of about 10%, PCE of the SPF-modified cells with the structure of ITO/SnO2/SPF/MAPbI3/spiro-OMeTAD/Au still remained 94% of the initial value. In contrast, the control cell without SPF only remained 31.1% of its initial efficiency after 29 days. The main reason for the stability enhancement is the adjustment of interfacial energy level, the crystallinity enhancement, and the removal of the interfacial defect of the perovskite layer by introducing the hydrophobic and smooth SPF interfacial layer. Deep electrical study on the PSCs discloses that the cell has low carrier transfer resistance, low leakage current density, and minor interfacial charge accumulation. What’s more, the short-circuit current density is improved, and PCE of 20.47% is achieved.

Achieving rapid extraction and equivalent transport of charge carriers is an effective way to improve the performance of perovskite solar cells (PSCs). Herein, a thiophene‐based zwitterionic conjugated polyelectrolyte (poly(5‐amino‐5‐carboxy‐3‐oxapentyl)‐2,5‐thiophene [POWT]) is introduced into PSCs as a hole‐transporting and interfacial material. The polyelectrolyte has a high hole mobility of 5.74 × 10−3 cm2 V−1 s−1 (similar to that of poly(triarylamine) [PTAA]) and compatible covalence level relative to the perovskite. Terminated with a zwitterionic pair of a‐amino acid, POWT layer builds up a weak double‐layer capacitance at the interface, which is not strong enough to induce the migration of MA+ ions in the perovskite layer. Deep electrical study on the PSC with the structure of indium tin oxide (ITO)/POWT/FA0.2MA0.8PbI2.9Br0.1/C60/bathocuproine (BCP)/Ag discloses that the device has low carrier transfer resistance, low leakage current density, and minor interfacial charge accumulation. The open‐circuit voltage and the short‐circuit current density are much improved, and the power conversion efficiency (PCE) is up to 17.5%. With a‐amino acid zwitterions, POWT passivates the surface charge defects and grain boundaries of the perovskite film. The PSC presents negligible hysteresis and high stability. After 56 days, the unencapsulated PSC still remains at 85% of the original efficiency.