  This study investigated the electronic structure of SrTi$_{1-x}$V$_x$O$_3$
(STVO) thin films, which are solid solutions of strongly correlated transparent
conductive oxide (TCO) SrVO$_3$ and oxide semiconductor SrTiO$_3$, using ${in
situ}$ photoemission spectroscopy. STVO is one of the most promising candidates
for correlated-metal TCO because it has the capability of optimizing the
performance of transparent electrodes by varying ${x}$. Systematic and
significant spectral changes were found near the Fermi level (${E_{\rm F}}$) as
a function of ${x}$, while the overall electronic structure of STVO is in good
agreement with the prediction of band structure calculations. As ${x}$
decreases from 1.0, spectral weight transfer occurs from the coherent band near
${E_{\rm F}}$ to the incoherent states (lower Hubbard band) around 1.0-1.5 eV.
Simultaneously, a pseudogap is formed at ${E_{\rm F}}$, indicating a
significant reduction in quasiparticle spectral weight within close vicinity of
${E_{\rm F}}$. This pseudogap seems to evolve into an energy gap at ${x}$ =
0.4, suggesting the occurrence of a composition-driven metal-insulator
transition. From angle-resolved photoemission spectroscopic results, the
carrier concentration ${n}$ changes proportionally as a function of ${x}$ in
the metallic range of ${x}$ = 0.6-1.0. In contrast, the mass enhancement
factor, which is proportional to the effective mass (${m^*}$), does not change
significantly with varying ${x}$. These results suggest that the key factor of
${n/m^*}$ in optimizing the performance of correlated-metal TCO is tuned by
${x}$, highlighting the potential of STVO to achieve the desired TCO
performance in the metallic region.
