Base-catalyzed hydrolysis and condensation of zinc acetate dihydrate in alcoholic environments yields highly concentrated ZnO colloids with molarities near 3 M (50-70 wt % solid content) and particle sizes between 3 and 6 nm. These solutions were optimized to be stable against coagulation for several months and to yield optically transparent 0.8-2 mu m thick films of variable electronic conductivity in a single coating step. 2 atom % Al3+ or In3+, if present in these nanoporous air-sintered layers produce a high free-carrier concentration of about 6 x 10(19) cm(-3) without noticeable changes in sheet resistance R-sh > 10(6) Ohm square(-1), whereas sintering under vacuum or N-2/H-2 (90/10)-atmosphere results in R-sh values around 150 Ohm square(-1). Furthermore, infiltration of small ZnO clusters into the porous films increases the refractive index from 1.8 to 2.2 and substantially lowers R-sh to values of about 20 Ohm square(-1). From Hall measurements, the charge-carrier concentration has been determined to be 2 x 10(20) cm(-3) and the corresponding electron mobility approaches values of about 9 cm(2)/V s. Electron microscopic investigations revealed that the ZnO/Al crystallites have a typical size of 10 +/- 2 nm and are preferentially oriented with their (100) planes parallel to the substrate. Taking into account a preferential (002) orientation in physically deposited highly conductive ZnO/Al films, it appears that the chemical control of nanocrystallite boundaries is more decisive than their orientation within the films.