# Interface Engineering Strategies for Fabricating Nanocrystal-Based Organic-Inorganic Nanocomposites
## 1 Introduction  
Hybrid organic-inorganic nanocomposites, composed of semiconductor nanocrystals (NCs) and conjugated polymers (CPs), have garnered significant attention because they offer promising opportunities for the development of optoelectronic devices, including light-emitting diodes (LEDs) [1; 2], photovoltaic cells [3], sensors [4; 5; 6], and tunable lasers [7; 8; 9]. The size-dependent physical and chemical properties of NCs can be easily tailored by tuning their morphology and composition, paving the way for a wide range of opto-electronic applications [10; 11]. CPs have different advantages, including low weight, flexibility, solution processability, low cost, and large-area production [12; 13]. Moreover, organic-inorganic hybrid nanocomposites possess large interfacial areas, which can be beneficial to obtain high reactivity in solar cells and electrochemical applications [14; 15].  
In this context, different types of nanocrystals have been incorporated into the CP matrices. For example, semiconductor NCs (e.g., CdSe and PbS quantum dots (QDs)) have been mixed with CPs (e.g., poly(3-hexylthiophene) (P3 HT) and poly(2,6-bis(3-n-dodecylthiophen-2-yl)-alt-N-dodecyldithiophen[3,2-b-2,\({}^{\prime}\)3-d]pyrrole) (PDTPBT)) for photovoltaic applications [3; 16]. However, simple physical mixing of NCs and CPs often results in micro-scale phase agglomeration, which fails to fully exploit the large interfacial areas of NCs/CPs [8; 17; 18; 19; 20; 21; 22]. Moreover, the insulating aliphatic organic ligands capped on the NC surface hamper the electronic interactions between NCs and CPs.  
To overcome this problem, several approaches have been introduced for constructing organic-inorganic nanocomposites, including ligand refluxing, direct grafting methods, in situ growth of NCs in the presence of CPs, and template growth [23; 24; 25; 26; 27]. The direct grafting technique involves ligand refluxing with bifunctional ligands and chemical coupling with end-functionalized CPs. Pyridine or short-chain amines are generally used to introduce bifunctional ligands onto NC surfaces. In the in situ growth method, both nucleation and growth are initiated in the presence of CPs, yielding hybrid CP-NC nanocomposites. However, the precise control of NCs in the presence of CPs remains challenging.  
Conventional ligand refluxing often results in remnants of fatty aliphatic ligands on the NC surface, despite repeated purification procedures, detrimentally affecting the opto-electronic performance [28]. To this end, ligand exchange methods have been introduced involving inorganic ligands, such as molecular metal chalcogenide complexes, chalcogenide ions, and halide ligands [29]. It is a simple yet effective route to completely remove the original insulating organic ligands and introduce the desired ligands on the NC surface. Compared with conventional ligand exchange approaches (e.g., pyridine and short-chain amines), ligand exchange using inorganic ligands effectively displace both covalently bonded ligands (i.e., X-type) and dative-bonded ligands (i.e., L-type) on the NC surface [29].  
This review seeks to summarize the recent progress in the surface treatment of NCs and the synthesis of organic-inorganic hybrid nanocomposites. The interfacial engineering of NCs, including purification, characterization, and development of synthetic techniques, has been presented. Furthermore, the advances in surface treatment, using inorganic ligands for the design of CP-NC nanocomposites, have been highlighted.