INFLUENCE OF LIGHT ABSORPTION PROFILE ON THE PERFORMANCE OF ORGANIC PHOTOVOLTAICS

Abstract

We investigate how an enhanced light absorption at a specific position inside the active layer affects the performance of organic photovoltaic cells (OPVs), namely the short-circuit current density ( ), the open-circuit voltage ( ), the fill factor (FF), and the power conversion efficiency (PCE). The performance is calculated using an updated version of a previously published analytical current-voltage model for OPVs, where the updated model allows the light absorption profile to be described by any functions provided that analytical solutions can be produced. We find that the light absorption profile affects the performance through the drift current. When the mobility imbalance is not very high (when the ratio of the mobility of the faster carrier type to the mobility of the slower carrier type is less than about ), the PCE is maximized when the light absorption is concentrated at the center of the active layer. When the mobility imbalance is very high (when the ratio of the mobility of the faster carrier type to the mobility of the slower carrier type is more than approximately ), the PCE is maximized when the light absorption is concentrated near the electrode collecting the slower carrier type. Therefore, it is important to ensure that the light absorption profile is properly tuned so that the performance of OPVs is maximized. Moreover, any efforts that we make to improve the performance should not lead to a light absorption profile that would actually impair the overall performance. ABSTRAK: Kajian ini menilai bagaimana penyerapan cahaya yang tinggi pada bahagian tertentu lapisan aktif mempengaruhi prestasi sel fotovoltaik organik (OPV), iaitu ketumpatan arus litar pintas (Jsc), voltan litar terbuka (Voc), faktor pengisian (FF), dan kecekapan penukaran kuasa (PCE). Prestasi dikira mengguna pakai model terkini yang diperbaharui dari model asal analitikal OPV voltan-arus, di mana model ini membenarkan mana-mana profil penyerapan cahaya digunakan asalkan penyelesaian analitikal terhasil.  Dapatan kajian mendapati profil penyerapan cahaya mempengaruhi prestasi berdasarkan arus hanyut. Apabila ketidakseimbangan pergerakan caj tidak begitu tinggi (di mana nisbah pergerakan pembawa caj laju kepada perlahan adalah kurang daripada 103), PCE menjadi maksimum jika penyerapan cahaya bertumpu pada tengah lapisan aktif. Apabila ketidakseimbangan pergerakan caj sangat tinggi (di mana nisbah pergerakan pembawa caj laju kepada perlahan adalah lebih daripada 104), PCE menjadi maksimum jika penyerapan cahaya bertumpu pada elektrod yang mengutip pembawa caj perlahan. Oleh itu, kedudukan talaan profil penyerapan cahaya yang tepat adalah sangat penting bagi menentukan prestasi OPV dimaksimumkan. Tambahan, apa sahaja usaha penambahbaikan prestasi seharusnya tidak menyebabkan pengurangan keseluruhan prestasi profil penyerapan cahaya.