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Perovskite solar cells (PSC) have emerged as a promising substitute for conventional silicon panels, showing the fastest power conversion efficiency evolution within the photovoltaic field, going from 3.8 % to 23.7 % in a few years. However, PSC thermal stability is still an obstacle to their commercialization. In this study, the temperature effect on mesoporous triple‐cation perovskite solar cells with two different hole extraction materials—2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene (spiro‐OMeTAD) and poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine] (PTAA)—is assessed. The cells are exposed to thermal stress between −5 °C and 80 °C and their photovoltaic performance is monitored in situ to reproduce real operating conditions. At low temperatures, the devices present very stable values (average loss <5 %), but as the temperature increases significant decreases in the open circuit potential and short‐circuit current are observed. X‐ray diffraction shows no change in the perovskite crystal structure with temperature. However, electron scanning microscopy and X‐ray photoelectron spectroscopy indicate that temperature has a great impact on the hole extraction layer. The cell performance loss is attributed to the evaporation of additives added to the hole extraction layer to enhance its conductivity. Although the decrease in power conversion efficiency at 80 °C is slightly higher for PTAA cells, spiro‐OMeTAD cells present a higher irreversible loss of (21.6±2.3) % after thermal stress tests, whereas PTAA devices showed only a loss of (8.2±1.6) %.

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Four novel heterocycle dyes 3a-d were synthesized in order to study the variations produced in the optical, electronic and photovoltaic properties by substitution of different electron-rich heterocyclic groups to the thieno[3,2-b]thiophene system. The final push-pull conjugated dyes 3a-d were synthesized by Suzuki-Miyaura coupling reaction followed by Knoevenagel condensation of the corresponding aldehyde precursors with cyanoacrylic acid 2a-d. These new push-pull systems are based on a thieno[3,2-b]thiophene spacer, a cyanoacetic acid anchoring group and several electron-rich heterocycles (thiophene, pyrrole and furan) as donor groups. The multidisciplinary study concerning the optical, redox and photovoltaic characterization of the dyes reveals that compound 3b bearing a hexyl-bithiophene donor group/heterocyclic spacer exhibits the best overall conversion efficiency (2.49%) as sensitizer in nanocrystalline TiO 2 dye sensitized solar cells. Co-adsorption studies between N719 and 3b revealed that upon addition of N719 co-adsorbent, the optimized cell efficiencies were improved by 16e77%. The best efficiency was 4.40%, corresponding to 54% of the photovoltaic performance of the N719-based DSSC fabricated and measured under similar conditions.

a b s t r a c tFive push-pull heterocyclic dyes 4e7, and 9 were synthesized and characterized in order to study the variations in the optical, electronic and photovoltaic properties induced by structural modifications, i.e. different spacer units and anchoring groups. The final push-pull conjugated dyes 6e7 and 9 are formed by a N,N-dimethylaniline donor moiety conjugated with bithiophene, ethynyl-bithiophene or ethynylthieno[3,2-b]thiophene spacers and cyanoacetic acid or rhodanine-3-acetic acid as anchoring group. The synthesis of the precursor aldehydes 4e5 was accomplished through a Sonogashira coupling, on the other hand, compound 8 was prepared by Suzuki coupling. Knoevenagel condensation of aldehydes 4, 5 and 8 with cyanoacetic acid or rhodamine-3-acetic acid afforded the final push-pull dyes 6, 7 and 9. Information on conformation, electronic structure and electron distribution was obtained by DFT and TDDFT calculations. This multidisciplinary study regarding the evaluation of the optical, redox and photovoltaic properties of the dyes reveals that compound 7, bearing an ethynyl-bithiophene spacer conjugated with a cyanoacetic acid anchoring group, has the highest conversion efficiency (3.51%) as dye sensitizer in nanocrystalline TiO 2 solar cells. Co-adsorption studies were also performed for dyes 6e7 with N719 as co-adsorbent, and this enhanced dye efficiencies by 33e45%. The best cell performance was obtained by co-adsorbing N719 and dye 7 (75/25 vol%) with 4.66% efficiency.