Photovoltaic properties of double-layer iso-type heterostructures based on pentacene, hexathiopentacene, and lead-phthalocyanine are studied. The heterostructures are prepared by thermal deposition on glass substrates at various substrate temperatures (T(s)). Under modulated illumination, the sign reversal is observed in photovoltage spectra of pentacene/lead-phthalocyanine heterostructures deposited at T(s) = 300K The properties of these structures are well described by the van Opdorp model for inorganic iso-type heterojunctions. No sign reversal has been observed in pentacene/lead-phthalocyanine, pentacene/hexathiopentacene, acene, and hexathiopentacene/lead-phthalocyanine heterostructures deposited at T(s) = 370K, the magnitudes of photovoltage being higher than those in structures prepared at T(s) = 300K.