Overcoming Moisture‐Induced Degradation in Organic Solar Cells

Abstract

Unencapsulated organic solar cells are prone to severe performance losses in the presence of moisture. Accelerated damp heat (85 °C/85% RH) studies are presented and it is shown that the hygroscopic hole‐transporting PEDOT:PSS layer is the origin of device failure in the case of prototypical inverted solar cells. Complementary measurements unveil that under these conditions a decreased PEDOT:PSS work function along with areas of reduced electrical contact between active layer and hole‐transport layer are the main factors for device degradation rather than a chemical reaction of water with the active layer. Replacements for PEDOT:PSS are explored and it is found that tungsten oxide (WO3) or phosphomolybdic acid (PMA)—materials that can be processed from benign solvents at room temperature—yields comparable performance as PEDOT:PSS and enhances the resilience of solar cells under damp heat. The stability trend follows the order PEDOT:PSS << WO3 < PMA, with PEDOT:PSS‐based devices failing after few minutes, while PMA‐based devices remain nearly pristine over several hours. PMA is thus proposed as a robust, solution‐processable hole extraction layer that can act as a one to one replacement of PEDOT:PSS to achieve organic solar cells with significantly improved longevity.

Stability of organic solar cells: toward commercial applications

“…1. 28,29 First, oxygen and moisture can significantly reduce the lifetime of OSCs; 30–32 however, this problem can be well addressed by the encapsulation technology. 33,34 Second, the actual reasons for device instability under irradiation are photochemical and photophysical degradation of the active layer, hole/electron transporting layer and active layer/electrode interface.…”

Células solares de terceira geração: estudo do efeito da degradação nos parâmetros fotovoltaicos

“…A degradação observada nos parâmetros fotovoltaicos está diretamente associada à presença de oxigênio e aos elevados níveis de umidade aos quais os dispositivos foram submetidos durante o teste. [117][118][119] A presença de oxigênio pode contribuir para a oxidação dos eletrodos, como é destacado em estudos anteriores 120,121 . Além disso, a umidade favorece a absorção de moléculas de H 2 O pelas camadas intermediárias, 63,122 prejudicando a eficiência da transferência de carga e a resposta fotovoltaica dos dispositivos.…”