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

Abstract

on poly(p-phenylenevinylene) (PPV) and CdTe nanocrystals (NCs) was developed. [2] This work demonstrated the important influence of hybrid on the performance of solar cells based on aqueous process, encouraging us to further investigate the ASCs with a new configuration.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, [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. are developed to address these issues. For example, Wei et al. successfully designed conjugated polymer with high carrier mobility and largely improved device performance. [15] Jin et al. achieved a record PCE of 5.64% (as reported) based on PPV and CdTe NCs by optimizing device structure. [16] However, controlling the width of the depletion region and enhancing carrier extraction ability have been long a challenge.To address these issues, our group further developed an effective strategy that introduced different BHJ structure into the active material. The highest PCE as high as 6.01% was achieved based on ASCs. [17] In that work, one BHJ is consisted of CdTe and TiO 2 NCs and the other is CdTe NCs and PPV. The width of the depletion region and carrier extraction ability were significantly improved compared to previous works. As known, within limits, the thicker the BHJ film is, the better the performance is. In organic solar cells, the BHJ thickness can even reach 210 nm. [18] For aqueous-processed hybrid solar cells (AHSCs), however, the optimum thickness of the CdTe:TiO 2 BHJ film is only ≈30 nm in the double-side bulk heterojunction system mentioned above. In order to increase the BHJ film thickness and form the bicontinueous phase, the content of TiO 2 NCs have to be enhanced because of their small size. However, TiO 2 NCs contribute no photocurrent in the range of visible light and hence further increasing the thickness of BHJ film leads to the decrease of J sc . Although employing TiO 2 NCs with a larger size can obtain a thicker BHJ film and alleviate the decrease of J sc in theory, preparing water-soluble annatase TiO 2 with larger size is difficult and the aggregation occurs during Environmental friendly aqueous-processed solar cells have become one of the most promising candidates for the next-generation photovoltaic devices. Researchers have made lots of progress in designing active materials with novel structures, manipulating the defects in active materials, optimizing device architecture, etc. However, it has long been a challenge to control the width of the depletion region and enhance carrier extraction ability. Fabrication of a thick bulk heterojunction (BHJ) film is an effective strategy to address these issues but difficult to realize. Herein...

Hole Transfer Layer Engineering for CdTe Nanocrystal Photovoltaics with Improved Efficiency

“…Recently, intensive investigations have been focused on CdTe NC solar cells with an inverted structure [ 4 , 5 ]. Comparing to the conventional CdTe NC solar cells using indium tin oxide (ITO) as the anode, devices with an inverted structure have many advantages, such as long-term stability under ambient conditions by avoiding the usage of low work-function metal cathode on the top of the device and better photon absorption efficiency due to the small distance between the active layer and the illumination source [ 6 , 7 ]. Due to the high resistance and low doping concentration of CdTe NC thin film, it is difficult to obtain a low resistance contact between CdTe and the back contact electrode [ 8 ].…”

Recent Progress in Hybrid Solar Cells Based on Solution-Processed Organic and Semiconductor Nanocrystal: Perspectives on Device Design

“…Benefiting from the advantages of increased carrier collection and lifetime, a PCE up to 6% was obtained in a champion device. Following this, this research group selected ZnO NCs and sol-gel ZnO as an acceptor/ETL to build an HSC with a device architecture of ITO/ZnO/CdTe:ZnO NC/CdTe/PPV:CdTe/MoO 3 /Au [60]. A high PCE of 6.51% was achieved, which was among the highest PCEs already reported for aqueous-processed CdTe NC HSCs.…”

Hybrid Nanocomposite Thin Films for Photovoltaic Applications: A Review

“…Chen (2019) employed CdTe nanocrystals (18 nm in size), ZnO nanocrystals (35 nm in size) and PPV in the development of PV cells with the same double-side BHJ architecture [ 216 ]. This time, the CdTe layer is simultaneously sandwiched between the ZnO:CdTe BHJ (increase the electron extraction ability) and the CdTe:PPV BHJ (increase the hole extraction ability).…”