We present new stilbazolium salt DSTMS (4-N,N-dimethylamino-4'-N'-methyl-stilbazolium 2,4,6-trimethylbenzenesulfonate) with both high second-order nonlinear optical properties and very favourable crystal growth characteristics. We are able to obtain very large area bulk single crystals of more than 3 x 3 x 0.2 cm(3) with a high optical quality without using seed crystals by using low-temperature solution growth. We also demonstrate the growth of single crystalline thin films of DSTMS with an area of up to 6 x 5 mm(2) and a thickness between 5-30 mu m. Nonlinear optical measurements reveal that DSTMS possesses large non-linear optical susceptibilities with chi((2))(111) = (430 +/- 40) pm V-1 at 1.9 mu m. Highly efficient generation of broadband THz waves with THz electric field strengths of more than 4 kV cm(-1) using 160 fs laser pump pulses at a wavelength lambda = 1.45 mu m and DSTMS crystals has been demonstrated.