Donor–acceptor nanocomposite structures for organic photovoltaic applications

Abstract

We investigated the effect of substrate temperature T S on the growth of 80 nm donor-acceptor nanocomposite (DAN) layers consisting of co-evaporated Zn-phthalocyanine (ZnPc) and C 60 as absorber materials in organic solar cells. High temperature devices show lower series resistances R S but also reduced V OC . Both effects are diminished when the upper 20 nm of the blend are deposited at room temperature (RT). Moreover, the temperature profile improves the photocurrent density J SC .Best efficiencies (up to 2.1%) were achieved applying a 90 8C/RT profile. Transmission electron microscopy studies on the corresponding DAN revealed the temperature-dependent formation of crystalline C 60 phases (already at low T S ) and crystalline ZnPc phases (at highest T S ). The strong phase separation at 90 8C results in less compact and mechanical unstable films. Such devices exhibit low parallel resistance R P . When the cold cover layer is applied R P doubles.

Charge separation in organic semiconductor blends studied by electrical in situ characterization during film growth

“…The creation of good percolation pathways in the blends of higher crystallinity in the HOT films led to the observed improved charge carrier extraction and improved dissociation of excitons to generate light‐induced charge carriers. These results are in good agreement with improvements in solar cells of PcZn/C 60 blends following growth at elevated temperature 9, 10.…”

“…Post‐production current and heat treatments proved to be useful for device performance 6–8. Most promising efficiencies were reached by temperature variation during preparation of buckminster‐fullerene (C 60 )/phthalocyaninatozinc (PcZn) solar cells 9, 10. These developments have led to present record cell efficiencies of 8.3% for evaporated organic BHJ solar cells 11.…”

Why Inverted Small Molecule Solar Cells Outperform Their Noninverted Counterparts

“…[ 18,19 ] Due to the independence of exciton dissociation on applied voltage, the fi ll factor of solar cells with crystalline C 60 domains is expected to increase. [ 31 ] Such an increase in FF was indeed observed for inverted devices where the blend is deposited on a pristine C 60 layer, [ 11,22,32 ] whereas in this work and several others [ 12,13,23 ] no improvement for noninverted devices was achieved. We conclude that substrate heating is a necessary but not suffi cient prerequisite for an optimal BHJ composition.…”

“…This impressive gain has been spurred by improvements in device architecture, [ 5 ] processing, [ 6 ] materials, [ 7 ] and theoretical understanding. [ 8 ] The role of substrate heating during [ 9 ] or post [ 6 ] BHJ deposition and its impact on PCE via changing the morphology have been studied extensively from early on, however, with mixed results, leading to a clear improvement, [ 10,11 ] no change, or even a decrease [ 12,13 ] of PCE. Possible morphological effects of temperature treatments on BHJs can be roughly divided into three aspects: relative next neighbor orientation of donor/acceptor molecules, [ 14,15 ] mid-range phase separation, [ 16 ] and ordering in pure phase-separated regions.…”

Correlation between nanostructural, optical, and photoelectrical properties of P3HT:SiNW nanocomposites for solar‐cell application

“…The organic-inorganic nanocomposites are very promising for applications in devices such as light-emitting diodes, photodiodes, photovoltaic cells, and gas sensors. Applications of different organic-inorganic nanocomposites to organic solar cells [2][3][4][5][6][7][8][9][10][11][12][13] have been reported, particularly using silicon based nanostructures in organic matrix [14][15][16][17].…”