## 3 Results and Discussion
### Bilayer Planar Heterojunction  
Pentacene and C\({}_{60}\) are typical hole and electron transport materials with high mobility [29; 30]. To overcome the challenge of the low mobility of the PbPc film, a channel layer of either 30-nm-thick pentacene or C\({}_{60}\) was introduced, and the PbPc film was used \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Active Layer Structures** & \(\mu\)**a (cm\({}^{2}\)/V\(\cdot\)s)** & \(R\)**b (mA/W)** & \(P_{\text{max}}\) & \(D^{*}\) (Jones) & _EQE_ \\ \hline A: PbPc & \(8.5\times 10^{-4}\) & 4.43 & 9.3 & \(5.5\times 10^{9}\) & 0.65\% \\ B: pentacene/PbPc & \(3.0\times 10^{-2}\) & 139 & \(5.3\times 10^{3}\) & \(6.2\times 10^{10}\) & 20.29\% \\ C: C\({}_{60}\)/PbPc & \(3.9\times 10^{-2}\) & 142 & \(5.5\times 10^{3}\) & \(5.3\times 10^{10}\) & 20.73\% \\ D: pentacene/PbPc/C\({}_{60}\) & \(2.4\times 10^{-2}\) & 1415 & \(1.2\times 10^{4}\) & \(7.0\times 10^{11}\) & 206.55\% \\ \hline \hline \end{tabular}  
* Extracted from the following equation: \(I_{\text{d}}=(W/Z)\mu C_{\text{c}}(V_{\text{g}}-V_{\text{ph}})^{2}\), b The obtained results were acquired under the incident light power condition of \(3.44\) mW/cm\({}^{2}\) and \(V_{\text{d}}=-50\) V.  
\end{table} 
Table 1: Device parameter summary from the experiments. Figure 3: (**a**) Output and (**b**) transfer characteristics of the PbPc single-layer OPT (Dev-A) under both dark conditions and various incident light intensities. as the photoactive layer, that is, Dev-B and Dev-C. In Figure 4a,b, the output and transfer characteristics of Dev-B are presented, featuring the structure of Si/SiO\({}_{2}\)/pentacene (30 nm)/PbPc (20 nm)/Au. One can see that Dev-B has p-channel operation characteristics. In the dark, the \(I_{\rm d}\) of Dev-B at \(V_{\rm d}=V_{\rm g}=-50\) V is \(-693.78\) nA and rises to \(-1053.77\) nA under 3.44 mW/cm\({}^{2}\) illumination, and thus an \(I_{\rm ph}\) of 359.22 nA and an \(R\) of 139 mA/W are obtained, and the \(R\) of Dev-B is 32 times larger than that of Dev-A (Table 1). And at \(V_{\rm d}=-50\) V, a \(P_{\rm max}\) of 5.3 \(\times\) 10\({}^{3}\) of Dev-B is achieved, which is 570 times greater than that of Dev-A, and an EQE of 20.29% is acquired and bigger than that of Dev-A (see Table 1). The far superior performance of Dev-B to Dev-A is mainly ascribed to the higher NIR absorption and carrier mobility of Dev-B than Dev-A (see Figure 2 and Table 1), and the higher NIR absorption and carrier mobility of Dev-B benefit from the increased triclinic phase content and crystallinity of the PbPc films owing to template inducing of the pentacene layer [31]. In Figure 4c,d, we illustrate the output and transfer characteristics of Dev-C with a structure of Si/SiO\({}_{2}\)/C\({}_{60}\) (30 nm)/PbPc (20 nm)/Au, which show that Dev-C has n-channel operation characteristics. In the dark, the \(I_{\rm d}\) of Dev-C at \(V_{\rm d}=V_{\rm g}=50\) V is 806.63 nA and increases to 1173.24 nA under 3.44 mW/cm\({}^{2}\) illumination, and an \(I_{\rm ph}\) of 366.61 nA and \(R\) of 142 mA/W are gained, and the \(R\) of Dev-C is 33 times bigger than that of Dev-A (Table 1). And at \(V_{\rm d}=50\) V, a \(P_{\rm max}\) of 5.5 \(\times\) 10\({}^{3}\) of Dev-C is obtained, which is 591 times larger than that of Dev-A, and an EQE of 20.73% is obtained and greater than that of Dev-A (see Table 1). Clearly, the performance of Dev-C is much better than that of Dev-A, which is largely due to the higher carrier mobility and exciton dissociation efficiency of Dev-C than Dev-A, and the higher exciton dissociation efficiency of Dev-C is a result of the newly established exciton dissociation centers at the C\({}_{60}\) (acceptor)/PbPc (donor) interface. Due to relatively large energy barriers between the highest occupied molecular orbital (HOMO) levels and the lowest unoccupied molecular orbital levels of C\({}_{60}\) and PbPc, a strong C\({}_{60}\)/PbPc interfacial electric field will be formed, and the excitons diffusing to the C\({}_{60}\)/PbPc interface will be dissociated into free electrons and holes.