A block copolymer useful in electron beam and extreme ultraviolet photolithography includes a first block with units derived from a base-solubility-enhancing monomer and an out-of-band absorbing monomer, and a second block having a low surface energy. Repeat units derived from the out-of-ban absorbing monomer allow the copolymer to absorb significantly in the wavelength range 150 to 400 nanometers. When incorporated into a photoresist composition with a photoresist random polymer, the block copolymer self-segregates to form a top layer that effectively screens out-of-band radiation.