Titanium dioxide was extensively used in solar cell industry and currently has been studied to produce passivated contacts in PERC/PERT and TOPCon solar cells. The aim of this paper was to analyze the impact of the thickness of TiO2 thin films deposited by electro-beam evaporation on the weighted reflectance and the surface passivation on silicon solar cells. Thin films with different thicknesses were deposited to produce PERT solar cells, varying from 50 to 90 nm. The surface passivation was enhanced as the thickness was increased. For instance, at 400 nm, the internal quantum efficiency increased from 71% to 76% when the thickness of the TiO2 was augmented from 50 nm to 90 nm. The lowest weighted reflectance was obtained in samples with 80 nm thick TiO2 films. Considering the compromise between antireflection properties and surface passivation, the highest efficiency solar cells were produced with 80 nm thick TiO2.

Abstract The silicon solar cells achieved relatively low prices in the last years and to introduce a new structure in the PV industry, the amount of silicon per watt has to be reduced, requiring a cost-effective manufacturing process. The use of n-type solar grade silicon has the advantages of presenting higher minority carrier lifetime than p-type one and the absence of the boron-oxygen defects. The aim of this paper is to present the development of 100 μm thick n+np+ silicon solar cells with a selective p+ rear emitter formed by boron deposited by spin-on and an Al/Ag grid deposited by screen-printing. The firing temperature of Ag/Al (rear face) e Ag (front face) was optimized and the temperature of 840 °C produced the devices with higher efficiency. The solar cells presented efficiencies of 16%, achieving a low silicon consumption of 1.6 g/W, 40% lower than thick p-type devices produced by the same process.

RESUMO No custo de produção de uma célula solar, a lâmina de silício representa da ordem de 50 % do valor final do dispositivo. Para reduzir os custos, vem sendo proposta a diminuição das espessuras atuais de 180-200 µm para 100-120 µm. Embora o silício tipo p seja o mais usado na fabricação de células solares, este material é suscetível à degradação devido à interação boro-oxigênio. Os dispositivos fabricados em lâminas de Si tipo n, dopadas com fósforo não apresentam tal degradação e têm potencial de obtenção de altas eficiências devido ao maior tempo de vida dos portadores de carga minoritários. O objetivo deste trabalho é apresentar o desenvolvimento de células solares n+np+ fabricadas sobre lâminas de silício Cz (Czochralski) com 100 μm de espessura. Foram fabricados dispositivos finos com a estrutura n+np+ e comparados com os dispositivos n+pp+ fabricados em lâminas convencionais. A eficiência média alcançada foi de (14,6 ± 0,4) % e o dispositivo mais eficiente atingiu 15,3 %. O maior valor de eficiência ficou abaixo do obtido com estruturas n+pp+ de 200 μm de espessura, quando atingiu-se uma eficiência de 16,2 %. O principal parâmetro que reduziu a eficiência das células finas foi o fator de forma, que alcançou um valor máximo de 0,748. Embora a eficiência seja menor com as lâminas finas, obteve-se uma baixa relação massa/potência, de 1,5 g/W, valor que é aproximadamente 53 % inferior ao obtido quando foram usadas lâminas espessas tipo p.

ABSTRACT In the solar cell production cost, the silicon wafer represents roughly 50 % of the final value of the device. To lower the costs, the reduction of the current wafer thickness from 180-200 µm to 100-120 µm has been proposed. Although the p-type silicon is used to manufacture solar cells, it is susceptible to degradation due to boron-oxygen interaction. The devices manufactured in n-type silicon wafers doped with phosphorus do not present such degradation and has the potential of achieving higher efficiencies due to the larger minority charge carrier lifetime. The aim of this work is to present the development of n+np+ solar cells fabricated in Cz silicon wafers 100 μm thick. Thin devices were manufactured with the n+np+ structure and compared to n+pp+ devices manufactured in standard thick wafers. The average efficiency of (14.6 ± 0.4) % was achieved and the most efficient device reached 15.3%. The efficiency was lower than obtained with n+pp+ thick devices, which presented 16.2 %. The main parameter that reduced the efficiency of thin cells was the fill factor, which reached a maximum value of 0.748. Although the efficiency reached by thin n-type devices was worse than thick p-type ones, the former achieved a low mass/power ratio of 1.5 g/W, which is approximately 53 % lower than that obtained from thick p-type devices.