Designing different nanomaterials with new and useful properties required for developing day-to-day technologies has remained in the forefront of research for decades. Among these, semiconducting, light-emitting, plasmonic, photovoltaic, and magnetic properties are in the frontline. [1][2][3][4][5][6][7][8][9][10][11][12][13] Furthermore, materials with rectification properties remain one of the most demanding materials in recent times. [1][2][3][4][14][15][16][17] Very recently, semiconducting nanomaterials with tunable plasmonic absorption properties have also been reported; [5][6][7][8][18][19][20][21][22] these may further expand the already widespread applications of these nanomaterials in diverse research fields, including both in biology and device-based technologies. Hence, materials with several of these new properties are in demand for their implementation in different developing modern technologies.For designing nanomaterials, the colloidal synthetic method has remained unique and unbeatable to date. However, the classical mechanistic approach for fabricating these materials following this solution phase synthesis is more effective for tuning over a smaller range of dimensions, and produces mostly smaller-sized nanocrystals. Efforts to get larger-sized nanocrystals lead either to a wider size distribution or precipitation. Generally, this has been observed for 0D, 1D, or 2D crystal-growth processes. [23][24][25][26][27][28][29][30] Hence, designing of surface-ligand-capped nanomaterials with a wide range of size tunability that maintains their narrow size distribution throughout still remains challenging and requires more advanced synthetic methods.Confining the growth to 2D, we explore here the fabrication of nano-to microscale-tunable platelet-shaped Cu I phosphide as one of the upcoming materials associated with several new properties. This shows the band-edge absorption in the NIR spectral window, tunable surface plasmonic absorption in mid-IR window and also has the rectification properties required for possible exploration as photovoltaic material. Synthesis with such a wide tunable size range (ca. 1000 nm) has been performed by controlling the number of nucleations followed by rapid growth along two feasible directions. In the entire tunable regime, the size distribution remains narrow; the platelets maintain a hexagonal shape and retain single crystallinity. Moreover, unlike reported nanoplatelets made from various materials, these show several intriguing patterns of MoirØ fringes in their overlapping regions on the TEM grid. Finally, these p-type semiconducting platelets are explored to study their, photocurrent, photoresponse and photovoltaic activity under whitelight illumination.For the synthesis of copper phosphide, phosphine gas generated ex situ [31] has been explored as the phosphide source. This also helps to carry out the reaction at relatively moderate temperatures (200-230 8C). Using CuCl as Cu precursor, a mixture of alkylamine and trioctylphosphineoxide as solvent, and trioctylpho...