Toward Faster Organic Photodiodes: Tuning of Blend Composition Ratio

Abstract

The ability of a light‐sensor to detect fast variation in incident light intensity is a vital feature required in imaging and data transmission applications. Solution‐processed bulk heterojunction (BHJ) type organic photodiodes (OPDs) have gone through key developments, including dark current mitigation and longer linear dynamic range. In contrast, there has been less focus on increasing OPD response speed (f–3dB). Here, bulk heterojunction OPDs based on electron‐donating polymer poly[thiophene‐2,5‐diyl‐alt‐5,10‐bis((2‐hexyldecyl)oxy)dithieno[3,2‐c:3′,2′‐h][1,5]naphthyridine‐2,7‐diyl] (or PTNT) and electron‐accepting phenyl‐C71‐butyric acid methyl ester (or PC71BM) are reported. The intrinsic charge transport characteristics required for fast speed OPDs are discussed, and an analytical model for the same is developed. The OPDs present 0.8 MHz f–3dB under no applied voltage bias for a typical blend ratio of 1:1 by weight. It is shown that balanced electron and hole mobility is a critical criterion for faster speed OPDs, which can be realized by tuning the composition ratio of the bulk heterojunction. By tuning PTNT and PC71BM blend ratio, the f–3dB was successfully raised by more than quadruple to 4.5 MHz. The findings provide a tool to set device architecture for faster next‐generation light sensors.

Significant Dark Current Suppression in Organic Photodetectors Using Side Chain Fluorination of Conjugated Polymer

“…The peak R res values of PH, PF, and PF3 were 0.35, 0.36, and 0.29 A W -1 at 532 nm, respectively; these are remarkably higher than that of a commercial silicon photodiode (0.27 A W -1 ). [55] D* is defined as the achievable SNR for a 1 W signal from a detector with an active area of 1 cm 2 and an electrical bandwidth of 1 Hz. Photodetectors with a high-D* can detect small signals that compete with the detector noise.…”

Narrowband organic photodetectors – towards miniaturized, spectroscopic sensing

“…Saggar et al showed that the response speed of PTNT:PC 71 BM (50 wt%) is limited by the slow electron transport as compared to the hole transport. 159 By increasing the PC 71 BM concentration, the electron mobility was increased and the hole mobility slightly decreased. The balanced charge carrier mobilities led to an increase in the cutoff frequency, as shown in Fig.…”

Impact of Polymer Molecular Weight on Polymeric Photodiodes

“…The LDR of a photodetector, often referred to as the device's linearity regime, is given by the orders of magnitude of light intensity for which the corresponding photocurrent response is in linear proportionality, [36][37][38] and is given by:…”

“…For NEP, i noise was experimentally determined from the root-mean-square (RMS) of fluctuations over the current signal (measured as a function of time) under dark conditions (see Section S5, Supporting Information). [37] The RMS of dark noise, so evaluated, were 4.6 nA cm −2 for FBR:P3HT H , 2.8 nA cm −2 for FBR:P3HT M , and 1.7 nA cm −2 for FBR:P3HT L (Figure S5b, Supporting Information) under −0.5 V. With R λ of ≈0.15 A W −1 at 532 nm (Figure S2a, Supporting Information), results in NEP of 11.3, 18.7, and 30.7 nW cm −2 for OPDs containing P3HT L , P3HT M , and P3HT H , respectively. Interestingly, significant difference in saturating intensity is observed (see Figure 4a), with P sat for FBR:P3HT H based OPD being the highest at around 170 mW cm −2 under −0.5 V, whereas it was the lowest at around 8 mW cm −2 for FBR:P3HT L (summarized details of LDR in Table S2, Supporting Information).…”

“…This was done by taking fast Fourier-transform of the dark current (measured as a function of time) under specific applied voltage bias. [37,50] Figure S12, Supporting Information shows the measured PSD of OPDs at −0.5, −1.0, and −2.0 V applied voltage bias. The PSD decreases with increasing frequency, before reaching a steady value.…”