Efficiency Enhanced Hybrid Solar Cells Using a Blend of Quantum Dots and Nanorods

Abstract

The cell performance of organic‐inorganic hybrid photovoltaic devices based on CdSe nanocrystals and the semiconducting polymer poly[2,6‐(4,4‐bis(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b;3,4‐b′]‐dithiophene)‐alt‐4,7‐(2,1,3‐benzothiadiazole)] (PCPDTBT) is strongly dependent on the applied polymer‐to‐nanocrystal loading ratio and the annealing temperature. It is shown here that higher temperatures for the thermal annealing step have a beneficial impact on the nanocrystal phase by forming extended agglomerates necessary for electron percolation to enhance the short‐circuit current. However, there is a concomitant reduction of the open‐circuit voltage, which arises from energy‐level alterations of the organic and the inorganic component. Based on quantum dots and PCPDTBT, we present an optimized organic–inorganic hybrid system utilizing an annealing temperature of 210 °C, which provides a maximum power conversion efficiency of 2.8%. Further improvement is obtained by blending nanocrystals of two different shapes to compose a favorable n‐type network. The blend of spherical quantum dots and elongated nanorods results in a well‐interconnected pathway for electrons within the p‐type polmer matrix, yielding maximum efficiencies of 3.6% under simulated AM 1.5 illumination.

Polymer selection toward efficient polymer/PbSe planar heterojunction hybrid solar cells

“…Polymers can offer high absorbance coefficient and excellent film-forming ability while NCs may provide tunable bandgap across visible to near infrared (NIR) and high carrier mobility [1,2]. A variety of inorganic NCs have been studied in HSCs such as cadmium chalcogenides NCs (CdS [3,4], CdSe [5,6], CdTe [7,8]) and lead chalcogenides NCs (PbS [9][10][11], PbSe [12], PbSSe [13]). Compared to cadmium chalcogenides, PbS and PbSe have significant larger exciton Bohr radii (PbS 20 nm, PbSe 46 nm, CdSe 6 nm) [14] and hence demonstrate higher carrier mobility (PbSe 0.9-7 cm À2 V À1 S À1 [15][16][17][18], CdSe $10 À2 cm À2 V À1 S À1 [19]) even without high temperature sintering.…”

In situ syntheses of semiconducting nanoparticles in conjugated polymer matrices and their application in photovoltaics.

“…Today, the highest efficiencies reported for hybrid solar cells are around 4% [5][6][7][8], which is still far away from the efficiencies of above mentioned technologies, but the progress in PCE in the last years and the conceptual advantages make it more and more realistic to approach the long-term goal of cheap, efficient and stable hybrid solar cells in future.…”

“…They studied charge [29] or zinc oxide [30], medium bandgap materials like cadmium sulfide [31], selenide [8,32,33] or telluride [34], copper indium sulfide [35] and selenide [36], as well as low band gap materials like lead sulfide [6], or selenide [37]. Recently, also other abundant and non-toxic materials like SnS 2 [38], FeS 2 [39] or Bi 2 S 3 [40] as well as silicon nanoparticles [41] have been researched concerning the incorporation in hybrid solar cells.…”

Colloidal Inorganic–Organic Hybrid Solar Cells

“…It has been proposed that QDs can disrupt the in-plane nanorod stacking and can also form connections between parallel lying nanorods to achieve better percolation pathways in the vertical direction. This method has been shown by different authors to increase J SC and FF compared to hybrids using only quantum dots or nanorods, leading to overall higher PCE, [32,33] but care must be taken that the offset in energy levels of the different NCs does not adversely affect V OC .…”