Ukrainian Journal of Physical Optics 

Volume 21, Issue 4, 2020
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Suppression of hot carriers by nanoporous silicon for improved operation of a solar cell

1 Ašmontas S., 2 Fedorenko L., 2 Vlasiuk V., 2 Gorbanyuk T., 2 Kostylyov V., 2 Lytovchenko V., 1, 3 * Gradauskas J., 1 Sužiedėlis A., 1 Širmulis E., 1 Žalys O. and 3 Masalskyi O.

1Center for Physical Sciences and Technology, Saulėtekio Avenue 3, 10257 Vilnius, Lithuania, info@ftmc.lt

2V. E. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, Nauky Avenue 41, 03028 Kyiv, Ukraine, info@isp.kiev.ua

3Vilnius Gediminas Technical University, Saulėtekio Avenue 11, 10223 Vilnius, Lithuania, vgtu@vgtu.lt

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Abstract. The surface of a silicon solar cell is modified to improve its photovoltaic characteristics. Nanostructured porous silicon layer is formed on a front n+-type surface of a p–n junction by means of electrochemical etching accompanied by illumination with a high-power light-emitting diode operating at the wavelength of 365 nm. Addition of the porous layer results in considerable increase in the capacitive photovoltage across the p–n junction. This increase is shown to be stipulated by reduced photonic losses due to anti-reflection coating effect of the porous layer, as well as by decreasing adverse effect of hot carriers on the photovoltage. Broadening of the spectrum of capacitive photovoltage towards the short-wavelength region was observed. This finding is associated with the graded-gap character of the porous layer and photovoltage formation across it as well as with increased absorption of high-energy photons in the porous layer and resulting weaker heating of free carriers.

Keywords: porous silicon, p-n junction, hot carriers, electrochemical etching, graded gap

UDC: 535, 621
Ukr. J. Phys. Opt. 21 207-214
doi: 10.3116/16091833/21/4/207/2020
Received: 06.11.2020

Анотація.  Поверхня кремнієвого сонячного елемента була модифікована для поліпшення його фотоелектричних характеристик. На передній n+-типу поверхні p–n переходу був сформований наноструктурований шар пористого кремнію за допомогою електрохімічного травлення, яке супроводжувалося освітленням потужним світлодіодом, що працював на довжині хвилі 365 нм. Додавання пористого шару призводить до значного збільшення ємнісної фотонапруги на p–n переході. Показано, що це збільшення обумовлене зменшенням втрат фотонів внаслідок дії противовідбивного покриття пористого шару, а також зменшенням несприятливого впливу гарячих носіїв на фотонапругу. Виявлено, що розширення спектру ємнісної фотонапруги в короткохвильову область. Це пов’язано зі варизонним характером пористого шару і сформованої фотоелектричної напруги на ньому та збільшенням поглинання високоенергетичних фотонів у пористому шарі та як результат зменшене нагрівання вільних носіїв.
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