A model of a p-n junction in the area of the grain boundaries in polycrystalline p-n structures is proposed. Shown mechanism of formation of impurity thermal-voltaic and impurity thermal-photovoltaic effects in IGB.A concept of creating highly effective comparatively inexpensive solar energy converters will be justified by the results we obtained during the study of the ITPV and ITV effects. Proposed theoretical model and experimentally obtained results can be useful in study of poly-Si n+-p structures, for example during external treatment. They allow explaining why in certain temperature ranges, an additional local heating, or applied potential, or a local illumination of pre-heated surface of poly-Si n+-p structure containing deep level impurities, can dramatically change the flow of current. In other words, such external treatment become trigger mechanism for discharge of charges accumulated in IGB due to impurity related thermal voltaic or thermal and photo-voltaic effects.