Displacement of energy-related carbon dioxide emissions crucially depends on developing low-cost and widely accessible routes to clean energy generation. From all renewable energy sources, solar energy has by far the greatest potential. However, the inorganic solar cells available on the market are currently too expensive to compete with conventional power sources. Hybrid inorganic–organic SCs are an emerging technology holding great potential for cheap fabrication. Based on a nano-structured junction, they combine cheap and abundant organic materials with the advantages of inorganic materials in terms of stability and charge transport. The EU-funded project 'Characterisation of hybrid inorganic-organic solar cells by advanced spectroscopic methods' (CHOIS) sought to further enhance understanding of the hybrid SC's working mechanisms to ultimately achieve high conversion efficiencies. Initially, scientists characterised a state-of-the-art hybrid cadmium sulphide (CdS)–polymer system through transient absorption spectroscopy. Results showed that excitations in CdS have a longer lifetime, leading to the conclusion that charge generation is not limited to small domain sizes. Scientists also found the main loss processes limiting charge generation in the polymer used. The next step was to use an inorganic material with a broader absorption spectrum to harvest more of the solar spectrum. Given their broader absorption spectra, antimony and bismuth sulphides were identified as promising alternatives to CdS, with the former exhibiting higher conversion efficiencies. Its minimised energy losses were attributed to charge separation. Based on these findings, scientists proposed new material combinations to produce more efficient hybrid SCs. Dense layers of antimony sulphide were fabricated and tested in SCs with a polymer as a hole conductor, demonstrating efficiency of above 3 %. Given that the inorganic material was the main active component, such SCs were classified as solution-processed inorganic. CHOIS contributed to further enhancing understanding of the mechanisms of hybrid SCs and determining a way to fabricate efficient ones. This should promote development of hybrid SCs with a solution-processed heterojunction, paving the way to producing alternative and inexpensive SCs.
Solar cells, hybrid solar cells, hybrid inorganic–organic, spectroscopic methods