Enhancement
of Performance and Mechanism Studies of All-Solution Processed Small-Molecule
based Solar Cells with an Inverted Structure
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Abstract
Both
solution-processed polymers and small molecule based solar cells have
achieved PCEs over 9% with the conventional device structure. However,
for the practical applications of photovoltaic technology, further
enhancement of both device performance and stability are urgently
required, particularly for the inverted structure devices, since this
architecture will probably be most promising for the possible coming
commercialization. In this work, we have fabricated both conventional
and inverted structure devices using the same small molecular donor/acceptor
materials and compared the performance of both device structures,
and found that the inverted structure based device gave significantly
improved performance, the highest PCE so far for inverted structure
based device using small molecules as the donor. Furthermore, the
inverted device shows a remarkable stability with almost no obvious
degradation after three months. Systematic device physics and charge
generation dynamics studies, including optical simulation, light-intensity-dependent
current–voltage experiments, photocurrent density-effective
voltage analyses, transient absorption measurements, and electrical
simulations, indicate that the significantly enhanced performance
using inverted device is ascribed to the increasing of <i>J</i><sub>sc</sub> compared to the conventional device, which in turn
is mainly attributed to the increased absorption of photons in the
active layers, rather than the reduced nongeminate recombination