Carrier-selective passivating contacts using transition metal oxides (TMOs) have attracted great attention for crystalline silicon (c-Si) heterojunction solar cells recently. Among them, tantalum oxide (Ta 2 O 5 ) exhibits outstanding advantages, such as a wide bandgap, good surface passivation, and a small conduction band offset with c-Si, which is typically used as an electron-selective contact layer. Interestingly, it is first demonstrated that solution-processed Ta 2 O 5 films exhibit a high hole selectivity, which blocks electrons and promotes hole transport simultaneously. Through the ozone pre-treatment of Ta 2 O 5 /p-Si interface and optimization of the film thickness (≈9 nm), the interfacial recombination is suppressed and the contact resistivity is reduced from 178.0 to 29.3 mΩ cm 2 . Moreover, the Sn 4+ doping increases both the work function and oxygen vacancies of the film, contributing to the improved hole-selective contact performance. As a result, the photoelectric conversion efficiencies of Ta 2 O 5 /p-Si heterojunction solar cells are significantly improved from 14.84% to 18.47%, with a high thermal stability up to 300 °C. The work has provided a feasible strategy to explore new features of TMOs for carrier-selective contact applications, that is, bipolar carrier transport properties.
You Liu,Fang Liu,Jungan Wang,Hongyan Huang,Suhao Yan,Song Gao,Lin Wang,Wei Huang,Tianshi Qin
Wide-bandgap photovoltaics (WBPV) could not only provide electrical energy by photoelectronic conversion of the invisible part of the solar spectrum, but also usually had the unique advantage of high open circuit voltage ( V oc). In this work, we reported a novel HTM based on tetrakis (N-phenothiazine) Spirobifluorene (Spiro-PT), its HOMO energy level could be well matched with MAPbBr 3 perovskite HOMO energy level. This HTM could effectively suppress nonradiative recombination, which leads to an increase in the photovoltage of WBPV to more than 1.41 V. As a result, the n-i-p mesoscopic structured WBPV achieved a champion PCE of 7.36% as well as excellent operational stability exhibiting 91% of initial efficiency after 500 h continuous illumination without encapsulation. Based on the high V oc of the MAPbBr 3 /Spiro-PT device, the photovoltaic electrochromic device showed a response speed (the average coloring time was 40 s and the bleaching time was 272 s) and high average visible light transmittance contrast (about 37% in 450–780 nm), the corresponding electrochromic device with maximum dynamic contrast up to 46% at 600 nm between bleached and colored states. This WBPV-powered electrochromic system could provide a pathway towards stand-alone smart window technique for future energy-saving buildings.
The electron/hole transport layer plays a very important role in the planar structure of perovskite solar cells. Conjugated polymers have received considerable attention for use in perovskite solar cells as hole/electron transport layers and passivation layers. Although the devices based on conjugated polymer hole transport layers have achieved much progress, their performance is still inferior to that of devices based on the conventional spiro-OMeTAD hole transport layer. Here, we investigated the solvent vapor annealing (SVA) effect on conjugated polymers as well as the corresponding perovskite solar cell devices. It was found that SVA treatment could enhance the hole charge carrier mobility and thin film crystallinity. Meanwhile, the charge transfer efficiency was enhanced, and charge recombination was reduced. Hence, the conjugated polymer based device exhibited comparable or even better performance compared with the conventional spiro-OMeTAD based device. Moreover, the device stability was also improved.
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