The use of mixed selective solvents provides an effective mean to control self-assembly of all-conjugated diblock copolymer poly(3-butylthiophene)-b-poly(3-hexylthiophene) (P3BHT) into nanostructured morphologies. The solvent and temperature effects on the self-assembly of P3BHT during cooling and subsequent crystallization were explored for the first time. Depending on the poor/good solvent ratio (i.e., anisole/chloroform), P3BHT chains experience different kinetic pathway and yield nanowires at low anisole/chloroform ratio, and nanowires of different width coexisted with nanorings at high anisole/chloroform ratio. Nanocomposites of poly(3-hexylthiophene)-cadmium selenide (P3HT-CdSe) were synthesized via a mild palladium-catalyzed Heck coupling, thereby dispensing with the need for ligand exchange chemistry. A click reaction to yield was P3HT-CdSe also explored. The resulting P3HT-CdSe nanocomposites possess a well-defined interface, thus significantly promoting the dispersion of CdSe within the P3HT matrix and facilitating the electronic interaction between these two components. The P3HT-CdSe nanocomposites at the air/water interface formed via Langmuir isotherms were studied. The photovoltaic devices fabricated from the LB depositions of the P3HT-CdSe nanocomposites exhibited a relatively high short circuit current, ISC, while maintaining a thin film profile.