Aqueous‐Processed Polymer/Nanocrystals Hybrid Solar Cells: The Effects of Chlorine on the Synthesis of CdTe Nanocrystals, Crystal Growth, Defect Passivation, Photocarrier Dynamics, and Device Performance

Abstract

High‐quality nanocrystals (NCs) are vital to achieve high‐performance polymer/nanocrystals hybrid solar cells (HSCs). However, in‐depth investigation on aqueous CdTe NCs related properties is extraordinarily insufficient, thus, limiting the further improvement of the device performance of aqueous‐processed HSCs. In this work, the effects of chlorine (Cl) on the synthesis of aqueous CdTe NCs, crystal growth, defect passivation, photocarrier dynamics, and device performance are systematically investigated. We demonstrate that the surface trap states of as‐prepared aqueous CdTe NCs can be effectively passivated by introducing Cl ions in the synthetic process. In addition, it is discovered that Cl in the as‐prepared CdTe NCs can promote CdTe grain growth in the sintered process to reduce grain boundaries. The aqueous‐processed poly(p‐phenylenevinylene) (PPV)/CdTe HSCs are used as prototype solar cells to systematically study the influence of Cl on the electrical properties of CdTe NCs. The power conversion efficiency (PCE) of the HSCs based on CdTe NCs with optimal Cl content is improved by a factor of 25 compared to that based on the CdTe NCs without Cl. The ultrafast transient absorption (TA), transient photovoltage (TPV) and light intensity dependent open circuit voltage (Voc) and short‐circuit current density (Jsc) measurements are implemented to systematically investigate the influence of Cl on photocarrier dynamics, including charge transfer, lifetime, and carrier recombination. The researches on carrier recombination indicate that the presence of Cl can effectively reduce nongeminate recombination to improve charge extraction efficiency, thus leading to elevated device performance. Furthermore, it is demonstrated that the residual Cl after annealing also plays important roles in the highly efficient polymer/CdTe HSCs by passivating the trap states on the grain boundaries of CdTe NCs. Finally, this work suggests that the photovoltaic performance of HSCs can be further promoted through adopting improved passivation methods to reduce trap states on the grain boundaries in the future work.

Highly Efficient Aqueous‐Processed Hybrid Solar Cells: Control Depletion Region and Improve Carrier Extraction

“…However, the performance of the ASCs is still severely limited by the narrow width of the depletion region, the intrinsic defects of NCs, and the low carrier extraction ability, resulting in low short‐circuit current ( J sc ) and open voltage ( V oc ) as well as a poor fill factor (FF). Many methods including passivating the surface of NCs, high temperature annealing, designing polymer with novel structure, optimizing device architecture, etc. are developed to address these issues.…”

“…Considering the influence of the thickness of BHJ on carrier separation, the transient photovoltage (TPV) measurement exhibited in Figure c is carried to explain carrier lifetime . It is obviously that Device A with a thicker film has a longer lifetime than Device B.…”

“…

on poly(p-phenylenevinylene) (PPV) and CdTe nanocrystals (NCs) was developed. Many methods including passivating the surface of NCs, [3][4][5] high temperature annealing, [6] designing polymer with novel structure, [2,[7][8][9][10][11] optimizing device architecture, [12][13][14] etc. Many methods including passivating the surface of NCs, [3][4][5] high temperature annealing, [6] designing polymer with novel structure, [2,[7][8][9][10][11] optimizing device architecture, [12][13][14] etc.

…”

“…A p-n heterojunction will be formed between n-type ZnO or TiO 2 and p-type CdTe. [3,30] It is obviously that Device A with a thicker film has a longer lifetime than Device B. Depletion region mainly consists of depletion region 1 (ZnO:CdTe or TiO 2 :CdTe BHJ film) and depletion region 2 (CdTe film).…”

Green-solvent-processed hybrid solar cells based on donor–acceptor conjugated polyelectrolyte

“…For example, Yang's group developed an effective method to form conjugated polymers by spincoating and thermal annealing the aqueous precursors. [15][16][17][18][19][20] Nevertheless, this method requires a long time annealing process to realize the polymerization. And the thermally cleavable side sites limited the choice of polymer precursors in certain types of units.…”