Thiocyanate‐ and Thiol‐Functionalized p‐Doped Quantum Dot Colloids for the Development of Bulk Homojunction Solar Cells

Abstract

Progress in device engineering and surface passivation strategies has led to steady progress in colloidal quantum dot (QD) solar cells. Bulk homojunction (BHJ) device architecture has several advantages over the conventional planar junction in developing QD solar cells. Herein, surface ligand chemistry is utilized to control the doping type and dispersibility of oppositely doped PbS QDs to develop BHJ solar cells. Thiocyanate and thiol ligand combination is introduced to develop p‐PbS QD ink, which is blended with halide‐passivated n‐PbS QDs to build BHJ solar cells. It is shown that BHJ solar cells are benefited from high energy offset and higher hole mobility. This leads to the superior carrier extraction from a thicker active layer without compromising fill factor and open circuit voltage. Power conversion efficiency has reached 10.7% in 530 nm‐thick BHJ solar cells, a 24% improvement over the best performing planar solar cells. With the help of the 1D solar cell capacitance simulator, it is shown that a 15% efficient QD solar cell can be realized by further improving the hole mobility above 0.1 cm2 V−1 s−1.

Multi‐Bandgap Quantum Dots Ensemble for Near‐Infrared Photovoltaics

“…Further, the E c and E v values for pPbS QDs (3.83 and 4.90 eV) appear at shallower energy values compared to nPbS QDs (4.09 and 5.05 eV), which suggests that in the mixed QD films, they will form type-II alignment at their interface. [27,37] In the case of photoexcitation in mixed QD films, the photogenerated electron will preferably move from the pPbS to nPbS and vice-versa for the hole, as shown by arrows in Figure 2b.…”

“…We measured electron and hole mobility for nPbS and pPbS QD solids using the space charge limited conduction (SCLC) technique. [35,37] Figure 4b,c show the current density vs voltage plot for electron-only and hole-only devices. The electron mobility of nPbS (2.57 Â 10 À4 cm 2 V À1 s À1 ) is found to be higher than pPbS (1.31 Â 10 À4 cm 2 V À1 s À1 ), whereas, hole mobility of pPbS (8.54 Â 10 À4 cm 2 V À1 s À1 ) is higher than nPbS (4.28 Â 10 À4 cm 2 V À1 s À1 ).…”

“…[ 32,36 ] Advanced device platform like bulk‐heterojunction (BHJ) configuration has been explored by blending n‐type and p‐type QDs to improve the carrier transport length in QD solar cells. [ 27,35,37,38 ] Nanoscale range carrier segregation and carrier transport through separately doped material phases (electron through n‐type QDs and holes through p‐type QDs) improve carrier lifetime and reduce recombination in BHJ solar cells. [ 39–41 ] To build BHJ solid using large‐size NIR bandgap QDs, doping control and solution phase dispersion of n‐ and p‐doped QDs needs to be achieved simultaneously.…”

“…[32,36] Advanced device platform like bulk-heterojunction (BHJ) configuration has been explored by blending n-type and p-type QDs to improve the carrier transport length in QD solar cells. [27,35,37,38] Nanoscale range carrier segregation and carrier transport through separately doped material phases (electron through n-type QDs and holes through p-type QDs) improve carrier lifetime and reduce recombination in BHJ solar cells. [39][40][41] DOI: 10.1002/ente.202201375 Narrow bandgap quantum dots (QDs) are an important class of materials for near-infrared (NIR) optoelectronic devices owing to their size-tunable bandgap and chemical root processing.…”

The Synergy of Lead Chalcogenide Nanocrystals in Polymeric Bulk Heterojunction Solar Cells

“…From the application point of view, the ligand-exchanged reaction is regularly performed for acquiring the desired optoelectronic characteristics. Some of the examples include (i) controlling the composition of the NC surface, (ii) desired NC morphologies, (iii) enhanced charge carrier mobility, (iv) shifting the ionization energy and work function, , and (v) tuning band edge positions over 2.0 eV. , Table shows some common ligands used for device fabrication, altering the device efficiency differently. For example, MPA covered PbS NCs yield superior device performance relative to TBAI and EDT through enhanced carrier recombination lifetimes and V OC .…”