Multifunctional Fullerene Derivative for Interface Engineering in Perovskite Solar Cells

Abstract

In perovskite based planar heterojunction solar cells, the interface between the TiO2 compact layer and the perovskite film is critical for high photovoltaic performance. The deep trap states on the TiO2 surface induce several challenging issues, such as charge recombination loss and poor stability etc. To solve the problems, we synthesized a triblock fullerene derivative (PCBB-2CN-2C8) via rational molecular design for interface engineering in the perovskite solar cells. Modifying the TiO2 surface with the compound significantly improves charge extraction from the perovskite layer. Together with its uplifted surface work function, open circuit voltage and fill factor are dramatically increased from 0.99 to 1.06 V, and from 72.2% to 79.1%, respectively, resulting in 20.7% improvement in power conversion efficiency for the best performing devices. Scrutinizing the electrical properties of this modified interfacial layer strongly suggests that PCBB-2CN-2C8 passivates the TiO2 surface and thus reduces charge recombination loss caused by the deep trap states of TiO2. The passivation effect is further proven by stability testing of the perovskite solar cells with shelf lifetime under ambient conditions improved by a factor of more than 4, from ∼40 h to ∼200 h, using PCBB-2CN-2C8 as the TiO2 modification layer. This work offers not only a promising material for cathode interface engineering, but also provides a viable approach to address the challenges of deep trap states on TiO2 surface in planar perovskite solar cells.

The Progress of Interface Design in Perovskite‐Based Solar Cells

“…Recently Yaowen Li and co-workers [ 109 ] synthesized a triblock fullerene derivative PCBB-2CN-2C8, and modifi ed the TiO 2 surface accordingly. The improvement on the ETL also contributed to the device performance greatly (PCE over 15% with an aperture area >1 cm 2 , as mentioned above).…”

“…a) The normalized PCE decay of devices with/without CsCl modifi er upon UV irradiation. [ 109 ] Copyright 2015, American Chemical Society. [ 167 ] Copyright 2015, The Royal Society of Chemistry.…”

Molecular Interlayers in Hybrid Perovskite Solar Cells

“…Interlayers can also serve many other roles such as blocking charge [66,67] and improving the intimacy of the contact between two layers. [43] For example, small molecules with low lying HOMO can be used to modify the electron extracting layer.…”

Progress of interface engineering in perovskite solar cells

“…By annealing TiO2 at 1 atm oxygen partial pressure or pretreating TiO2 by O2 plasma, the original oxygen vacancy sites could be effectively filled and the hysteresis could be suppressed. Li and co-workers [30] synthesized a triblock fullerene derivative (PCBB-2CN-2C8) to modify TiO2 surface, significantly improving charge extraction from the perovskite layer (Figs 2c and d).…”