Hybrid solar cells have two meanings in the literature. A hybrid cell is defined as a multi-layer cell consisting of two or more cells of different types or generations. In the second sense, a hybrid is a combination of a photovoltaic panel and a solar collector (as described in chapter 7.6 PVT systems ). Hybrid cells in the first sense will be presented below.

The aim of photovoltaic engineers and researchers is to create a cell that is highly efficient, cheap, easy to manufacture and robust. Hybrid cells are intended to combine the advantages of different cell types.

The first cell type is organic-inorganic hybrid cells. These cells can be produced by modifying the morphology of the silicon nanostructure, i.e. nanostructures were made in silicon (made by nanospheric lithography) and combined with a conductive organic polymer referred to by the acronym PEDOT:PSS. This layer was modified with silicon dioxide \( SiO_{2} \) iand further processed and cleaned. A gold layer was used as the outer electrode. The cells produced achieved a short circuit current density of 39.1 \( \frac{mA}{cm^{2}} \).
It was also possible to fabricate a cell with a metal/ organic layer/silicon modified /Au architecture. The silicon was modified by injecting multi-walled carbon nanotubes (MWNTs) and poly(3-octylthiophene), an organic donor material, into the silicon [1].
Another example of organic-inorganic hybrids are organic cells doped with silicon nanowires (SiNWs) [2]. On the indium tin oxide electrode, layers of PEDOT:PSS (as a supporting layer) and - as an active layer - a mixture of poly(-3hexylthiophene, P3HT) and methyl ester of (6,6)-phenyl-C₆₁-butyric acid were deposited successively (by the method of uncoiling). Nanotubes have been injected into this layer.
The above-mentioned hybrid organic-inorganic cells achieved efficiencies of several percent. These are not far from the efficiencies of typical organic cells. In the above cases, an increase in short-circuit current density was observed, which in combination with high open circuit voltages is a promising result.

The second cell type studied is perovskite-silicon cells. Due to the complementarity of absorption spectra ( Fig. 1 ) [3], these are the most promising. They offer the hope of performance beyond the maximum efficiency of silicon cells while keeping production costs low. An example structure is shown in Fig. 2 (based on [3]).

The active layer of such cells consists of a silicon layer (bottom, deposited on a non-transparent electrode), an upper perovskite layer and a recombination layer between them. This type of interconnection made it possible to achieve efficiencies of up to \( 26\% \) [4].

The last type presented is polymer cells doped with inorganic quantum dots.
Its principle of operation is the same as that of organic cells. Quantum dots (QDs) increase the absorption of the system - the generation of charge carriers can be achieved by photons which are also absorbed in the inorganic material (dots). The addition of quantum dots is also intended to support the transport of electrons and holes across the LUMO and HOMO levels, as well as to increase charge conductivity. Additionally, acceptor inorganic materials are more stable than organic materials, which solves one of the biggest problems with organic photovoltaics - its instability. The principle of operation is similar to that of organic cells, except that the polymer acts as the donor and the quantum dots as the acceptor. A schematic representation of the cell is shown in Fig. 3 [5].